I’m working to further simplify my frequency counter design. This one is simpler than my previous design both in hardware and software! Here’s a video to demonstrate the device in its current state:

I utilize the ATMega48’s hardware counter which is synchronous with the system clock, so it can only measure frequency less than half of its clock speed. I solve this issue by dividing the input frequency by 8 and clocking the chip at 12mhz. This allows me to measure frequencies up to about 48MHz, but can be easily adapted to measure over 700MHz (really?) by dividing the input by 128. Division occurs by a 74HC590 8-bit counter (not a 74HC595 as I accidentally said in the video, which is actually a common shift register), allowing easy selection of input divided by 1, 2, 4, 8, 16, 32, 64, or 128. The following image shows the o-scope showing the original signal (bottom) and the divided-by-8 result (top)

The device outputs graphically to a LCD simply enough. That LCD is from eBay and is only $3.88 shipped! I’m considering buying a big box of them and implementing them in many more of my projects. They’re convenient and sure do look nice!

The signal I test with comes from an oscillator I built several months ago. It’s actually a SA612 style receiver whose oscillator is tapped, amplified, and output through a wire. It’s tunable over almost all of 40m with a varactor diode configuration. It was the start of a transceiver, but I got so much good use out of it as a function generator that I decided to leave it like it is!

THIS IS HOW THE PROGRAM WORKS: I don’t supply a schematic because it’s simple as could be. Divide the input frequency to something relatively slow, <1MHz at least. Configure the 16-bit counter to accept an external pin as the counter source (not a prescaled clock, as I often use in other applications). Then set the timer value to 0, _delay_ms() a certainly amount of time (1/10th second), and read the counter value. Multiply it by 10 to account for the 1/10th second, then multiply it by 8 to account for the divider, and it’s done! It will update 10 times a second, with a resolution down to 10*8 = 80 Hz. It’s well within the range of amateur radio uses! If you’re considering replicating this, read up on how to use hardware counters with ATMEL AVR microcontrollers. That should be enough to get you started! Here’s the code I used…

For the LCD, this code requires LCD library.

#include <stdlib.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
#include <util/delay.h>
#include "lcd.h"
#include "lcd.c"

int main(void)
	TCCR1B=0b00000111; // rising edge trigger
    char buffer[8];
	long toshow=0;
	char mhz=0;
	int khz=0;
	int hz=0;

		itoa(mhz , buffer, 10);

		if (khz<100){lcd_puts("0");}
		itoa(khz , buffer, 10);

		itoa(hz/100 , buffer, 10);

		lcd_puts(" MHz");

		toshow=(long)toshow*16*10; // tenth second period

Additional Resources



UPDATE: Check out what happened when I revisited this project and made it wireless two years later!:




This page describes a method of sending data from a microchip to a PC using pulses of data. It’s an alternative to more traditional serial or USB methods of connectivity. It’s not intended as a solution for consumer products, but rather an easy hack for hobbyists to employ if they don’t have the equipment for other methods. This method doesn’t require *any* circuitry, just a sound card. The one built in your computer is fine, but I’m using a $1.30 USB sound card for simplicity. It boils down to just a single microcontroller pin connected to a PC sound card microphone jack!

UPDATE: This story was featured on this post of HackADay.com!

This is the finished product ready to send data to a PC:DSCN1532

MY PROBLEM: I want to send data from a simple microcontroller to a PC. While USART and a serial port is the common solution like I’ve done before, it’s not convenient because it requires a level converter (like a MAX232, about $4), crystal (specific values based on bit and error rate, if you’re lucky you might have a right value in your junk box), and an archaic PC which actually has a serial port. A usb serial port adapter sounds clever, but many aren’t supported on Linux, Windows Vista, or Windows 7. Also, many small chips (most of the ATTiny series) don’t have built in serial capabilities, so it has to be bit-banged in software! Yuk! The second choice would be USB. This requires a crystal too, zener diodes, and bit-banging the USB protocol with something like V-USB since most of the AVR series don’t have built in USB (do they even make breadbordable DIP chips with USB?). Even so, it requires drivers, custom software, cross-platform frustrations, etc. I know PIC has some 18f series chips with USB, but I don’t feel like switching architectures just to send a few bytes of data to a PC. FDTI has a FT232R chip which is a USB serial port adapter, but it’s expensive (about $5) and doesn’t come in dip, so no breadboarding! Sure there are adapter boards, but that just adds the cost. I’m not excited about a $5 solution for a $1 microcontroller. I even did a bit of trolling on AVR Freaks to see if anyone could help me out – just more of the same!

MY SOLUTION: Send data through the sound card! USB sound cards are $1.30 (shipped) on eBay! It couldn’t be simpler. Send pulses, measure distance between pulses. Short pulses are a zero, longer ones are a 1, and very long pulses are number separators. A Python solution with PyAudio allows 1 script which will work on Mac, Linux, Windows, etc, and because it calibrates itself, this will work on any chip at any clock rate. Data is initiated with calibration pulses so timing is not critical – the PC figures out how fast the data is coming in. Check it out! (scroll way down for a bidirectional communication solution)

Here is a sound card I used for bidirectional communication:
DSCN1466 DSCN1470

Output graph (python and excel) of temperature when I put a soldering iron near the sensor: pythonexcel


The following code is designed to have a chip send data to your PC automatically. This can be run on any micro-controller (PIC or AVR I guess, the concept is the same) at any clock rate. Just make sure the sound card is recording fast enough to differentiate pulses. (keep scrolling down for a bidirectional solution)

A NOTE ABOUT MY CODE: This is just the code I used for my demonstration. It might be more logical for you to write your own since the concept is so simple. I’m a dental student, not a programmer, so I’m sure it’s not coded very elegantly. I didn’t work hard to make this code easy to read or easy to share. With that being said, help yourself!

/*The following code is written in AVR-GCC for an ATTiny44a.
It reads ADC values on 3 pins and reports it each second along
 with a number which increments each time data is sent.
It's designed as a starting point, allowing anyone to
customize it from here!*/

#include <avr/io.h>
#include <avr/delay.h>
#include <avr/interrupt.h>

// bytes we want to send to the PC
volatile int data1=0;
volatile int data2=0;
volatile int data3=0;
volatile int data4=0;

void solid(){  // dont touch
	pulse(3);pulse(5);pulse(5);// CALIBRATION PULSES
void pulse(char size){ // dont touch
	while (size){size--;_delay_us(100);}
void sendVal(unsigned long tosend){ // dont touch
	pulse(5); // send a space
	while (tosend){
		if (tosend&1){pulse(3);} // send ONE
		else {pulse(1);} // send ZERO

int readADC(char adcNum){
	ADMUX=adcNum; // select which ADC to read, VCC as ref.
	ADCSRA=0b11000111; // enable, start, 128 prescale
    while (ADCSRA&( 1<<ADSC)) {}; // wait for measurement
	return ADC;

void takeReadings(){
        data1=readADC(0); // ADC0
        data2=readADC(1); // ADC1
        data3=readADC(2); // ADC2
		data4++; // incriment just because we want to

void sendStuff(){ // EDIT to send what you want
	solid(); //required
	sendVal(12345); //required
	sendVal(12345); //required
	sendVal(54321); //required


	pulse(1); //required

int main(){
	for (;;){
	return 0;
file name: listenOnly.py

This is the PC code to listen to the microphone and display
and log the data. It probably does NOT need adjustment!
 Make sure the correct sound card is selected (in the code)
 and make sure microphone input is turned up in volume control.

This code is what was used on my PC for the demonstration
video. This is the listenOnly.py file which will turn any audio
 detected from a sound card into data, optionally logging it
(if the last few lines are uncommented). This also works to
capture data for the bidirectional communication method,
described below on this website.

If this is running but no data is coming through, make sure the
microphone is selected as a recording device, the correct sound
card is selected, and the microphone volume is turned to high.

REQUIRED: To run this, you need to have the following installed:
-- Python 2.6
-- numpy for python 2.6
-- matplotlib for python 2.6
-- pyaudio for python 2.6
(other versions may work, but this is what I'm using)
import numpy
import pyaudio
import matplotlib.pyplot as plt
import wave
import time

def listCards(dontAsk=True):
    print "SOUND CARDS:"
    for i in range(p.get_default_host_api_info()["deviceCount"]):
        if p.get_device_info_by_index(i)["maxInputChannels"]>0:
                cardName = p.get_device_info_by_index(i)["name"]
                cardIndex = p.get_device_info_by_index(i)["index"]
                print "[%d] %s"%(cardIndex,cardName)
    if dontAsk: return
    return int(raw_input("CARD NUMBER TO USE:"))

print "USING CARD:",cardID


def data2vals(data):
    for i in range(1,len(data)):
        if data[i]==True and data[i-1]==False:
            if lastPeak>0: vals=numpy.append(vals,i-lastPeak)
    return vals

def binary2dec(binary):
    for i in range(len(binary)):
    #print s,"=",dec #11111100101100000 = 3391
    return dec

def readVals(vals):
    if len(vals)<7: return False
    aLow = min(vals[0:3])
    aMed = min(vals[3:6])
    aHigh = vals[6]
    #print "tresholds:",thresh1,thresh2
    #print vals
    for i in range(len(vals)):
        if vals[i]>thresh2:
        if vals[i]>thresh1:binary=[1]+binary
    for i in range(len(vals2)):
        if vals2[i]==54321: return vals2[i+1:]
    return False

def playFile():
    chunk = 1024
    wf = wave.open("short_onenum.wav", 'rb')
    p = pyaudio.PyAudio()
    stream = p.open(format =
                    channels = wf.getnchannels(),
                    rate = wf.getframerate(),
                    output = True)
    data = wf.readframes(chunk)
    while data != '':
        data = wf.readframes(chunk)

def captureData():
    pyaud = pyaudio.PyAudio()
    stream = pyaud.open(format=pyaudio.paInt16,channels=1,
        rate = 44100,input_device_index=cardID,input=True,output=True)
    while True:
        if True in sampleNew: sample=numpy.append(sample,sampleNew)
            if len(sample):
                return sample


def buildNumber(num=123):

    if num>255: print "NUMBER TOO HIGH!!!"
    #print num,'=',
    for i in [7,6,5,4,3,2,1,0]:
        if num>2**i:one();num=num-2**i;#print"1",
        else: zero();#print"0",

def pulse():
    global data

def space():
    global data

def one():
    global data

def zero():
    global data

def silence(msec=1000):
    global data

def sendAudio(numbers=[11,66,77]):
    global data
    print "SENDING",
    for numba in numbers:
        print numba,

    p = pyaudio.PyAudio()
    stream = p.open(rate=44100, channels=1, format=pyaudio.paInt16,
                    input_device_index=cardID, output=True)

while True:
    if val == False: continue
    for item in val: line+=str(item)+","
    print i,line


What if we want to send data TO the microcontroller? The solution is a little more complex, but quite doable. Just add an extra wire to the sound card’s speaker output and attach it to PCINT0 (the highest level internal interrupt). This is intended for advanced users, and if you’re doing this you probably are better off with USB or serial anyway! … but heck, why not do it as a proof of concept!

Note that the USB sound card speaker output was not powerful enough to trigger the digital input pin of the AVR, so an inverting buffer was made from a single NPN transistor (2n3904). The hardware interrupt was attacked to the collector, and the collector was attached through +5V through a 220 ohm resistor. The emitter was grounded. The base was attached directly to the sound card output. I also tried running the sound card output through a small series capacitor (0.1uF) and biasing the base to ground through a 1Mohm resistor and it worked the same. Hardware, simple. Chip-side software… a little more complex.

### VIDEO ###

This code is what was used on my PC for the
 demonstration video. The listenonly.py file
 (above on site) was also used without modification.
import pyaudio
from struct import pack
from math import sin, pi
import wave
import random
import numpy
import time

maxVol=2**15-1.0 #maximum amplitude
p = pyaudio.PyAudio()
stream = p.open(rate=44100, channels=1, format=pyaudio.paInt16,
		input_device_index=1, output=True)

def pulseZero():
    global wvData
    wvData+=pack('h', 0)*30
    wvData+=pack('h', maxVol)

def pulseOne():
    global wvData
    wvData+=pack('h', 0)*40
    wvData+=pack('h', maxVol)

def pulseSpace():
    global wvData
    wvData+=pack('h', 0)*50
    wvData+=pack('h', maxVol)

def buildNumber(num=123):
    if num>255: print "NUMBER TOO HIGH!!!"
    for i in [7,6,5,4,3,2,1,0]:
        if num>2**i:

wvData+=pack('h', 0)*2000
pulseOne() #required before sending data


wvData+=pack('h', 0)*2000

while True:
	print "SENDING",
This code is what was used on my AVR
microcontroller for the demonstration video
#include <avr/io.h>
#include <avr/delay.h>
#include <avr/interrupt.h>

volatile long commandIncoming=0;
volatile char command1=0;
volatile char command2=0;
volatile char command3=0;
volatile char command4=0;
volatile char bitsGotten=0;

// timing thresholds are critical! Send pulses to the chip
// and have it report the time between them. Use this to
// determine the best threshold value for your application.
// The ones here must be changed if you run at a speed other
// than 1mhz or if you use different timings in PC software
#define thresh_low 100 // between this and the next
#define thresh_high 130 // is the range for a logical 'one'

// ######## OUTGOING AUDIO DATA #########
void solid(){
	_delay_ms(1); //LONG LOW
	pulse(3);pulse(5);pulse(5);// CALIBRATION PULSES
void pulse(char size){
	while (size){size--;_delay_us(100);}
void sendVal(unsigned long tosend){
	pulse(5); // send a space
	while (tosend){
		if (tosend&1){pulse(3);} // send ONE
		else {pulse(1);} // send ZERO

// ######## INCOMING AUDIO DATA #########
SIGNAL (PCINT0_vect) { // audio input trigger
	TIMSK0|=(1<<TOIE1); //Overflow Interrupt Enable
	if (TCNT0<10){return;} // seem too fast? ignore it!
	// Enable the following line to test custom timings
	commandIncoming=commandIncoming*2; // shift left
	if (TCNT0>thresh_low){commandIncoming++;} // make 1

	if (bitsGotten){sendStuff();}

void fillCommands(){

void sendStuff(){
	TIMSK0=0; //Overflow Interrupt
	cli(); // disable interrupts!
	solid(); // start data transmissions with this
	sei(); // enable interrupts again!
	TIMSK0|=(1<<TOIE1); //Overflow Interrupt

// ######## MAIN PROGRAM #########
int main(){


	MCUCR = 0b00000010; // trigger interrupt on falling edge
	GIMSK = 0b00010000; // pin change interrupt enable 0
	GIFR =  0b00010000; // flag register, same as above
	PCMSK0 = (1<<PCINT0); // Set Pin to use (PCINT0)
	sei(); // enable global interrupts

	// SET UP 8-bit COUNTER
	//TCCR1B|=(1<<CS12)|(1<<CS10); // prescaler 1024
	TIMSK0|=(1<<TOIE1); //Enable Overflow Interrupt Enable
	TCNT0=0;//Initialize our varriable (set for 1/15th second?)

	for (;;){}
	return 0;


In closing, I’m tickled this works so well. It’s funny to me that no one’s really done this before in the hobby field. I’m sure I’m not the only one who wished there were an easy way to do this. I’m sure the process could be greatly improved, but this is a fun start. Wow, it’s late, I should get to bed. I have to treat patients tomorrow morning!

PS: If you replicate this concept, let me know about it! I’d love to see your project!

Additional Resources

My current secret project involves cramming a bunch of features into a single microcontroller. The chip I chose to use is an ATMega48. The ATMega 48 is $1.40 each in small quantities and comes crammed packed with features. The chip will be quite busy performing many functions, but its main loop will be executed at least every 50ms (required for USB, did I mention I’m bit-banging USB?!). I desire to have a bit of RTC (real time clock) functionality in that I need to precisely measure seconds, although I don’t need to actually know the time or date. I desire to execute a function once per second, consuming a minimum of resources. The solution was quite simple, but I’m choosing to document it because it’s somewhat convoluted in its explanation elsewhere on the net.

In summary, the way I accomplished this is using the built-in 16-bit timer (most AVRs have such a timer, including the ATTiny series). If I’m clocking the microcontroller at a known rate (determined by my selection of crystal, 12 MHz in my case), I can set the chip to continuously increment a register (timer1) and execute a function every time it overflows. Timer1 overflows at 2^16 (65,536). I enabled a prescaler value of 256 so that it takes 256 clock pulses to increment the timer. 12MHz/256 = 46,875 Timer1 increments each second. Since Timer1 overflows at 65,536, if I initiate Timer1 at 18,661 (65,536-46,875), it will take 1 second exactly to overflow. Upon overflowing, I do something (maybe flip a LED on or off), and reset the Timer1 back to its starting value 18,661. Done! Without using an external RTC module or even an external crystal or asynchronous timer, we managed to execute a function every second on the second with minimal overhead, allowing the chip to do everything it wants in the rest of the time!

The following example is a little more specific, executing a function exactly 15 times a second, and executing another function (to flash an LED) exactly every 1 second. It should be self explanatory:

// This function is called every second on the second
volatile int count; // this should be global
	TCNT1=62411;//Initialize our varriable (set for 1/15th second)
	count++; //increment 1/15th second counter
		statusTOGGLE(); // do your event (flash a LED in my case)
		count=0;//reset global variable
// This is for ATMega48, consult datasheet for variations for different chips
// place this just inside main(), before your primary loop
TCCR1B|=(1<<CS12);// prescaler 256
TIMSK1|=(1<<TOIE1); //Enable Overflow Interrupt Enable
TCNT1=62411;//Initialize our varriable (set for 1/15th second)
count=0; //Initialize a global variable
sei(); // enable interrupts

I’m having a lot of fun spending time going through the datasheet of this chip. It has a lot of features, and some I didn’t really dig deeply into. Without giving away too much of my project, I’ll show some photos I’m excited to share. My project interfaces the PC through USB directly attached to 2 pins using no intermediate chips (wow!). The photos demonstrate various steps in the temperature measurement and calibration tests…

Additional Resources

I did this purely for the fun of it, and am aware there are many ways to accomplish the same thing. I was playing Counter Strike Source (you should buy it and play with me, name “swharden”) and my fingers are really cold from the winter weather, and wondered if I could have a button help with the rapid firing of pistols. I mentioned it on the microphone, and one of the players (“{Ẋpli¢it} shadow”) said I should go for it. Because it was a fun little project, I documented it so I could share it. Check out the cool photos and video!

There’s a summary of the project in video form. Some details of the project are below…rapidfire_mouse_mod (1)

Here you can see the original circuit board in the mouse. The microchip on the bottom right of the image seems to do the data processing, so I investigated it a bit and found the pin that the left-click button goes to.rapidfire_mouse_mod (2)

Here’s the underside. It helped me identify good locations to grab +5V and GND solder points.rapidfire_mouse_mod (3)

This is the microcontroller I decided to use for the project. It’s an ATTiny25, $1.33 USD (10+ quantity from Mouser), and has a built in 8MHz oscillator (which can run at 1MHz thanks to the DIV/8 clock prescaler.rapidfire_mouse_mod (4)

I slap the chip in the homebrew development board (a glorified AVR-ISP mkII) and it’s ready for programming. Code and schematics are at the bottom.rapidfire_mouse_mod (5)

After programming, I glued the microchip upside-down in the mouse case and soldered wires directly to the pins. I used small (about 28AWG) magnet wire because it’s a lot easier than stripping wires. Just heat the tip with a soldering iron, the coating melts away, and you can stick it wherever you need to with a dab of solder. Not too many people use this method, but I recommend you try it at least once! It can be very useful at times, and is about as cheap as you can get. (eBay has good prices)rapidfire_mouse_mod (6)

BIG PROBLEM! It didn’t work *AT ALL*. Why? Didn’t know… I checked the o-scope and saw everything seemed to be working fine. It turns out that 50 clicks per second was too fast to register, and when I reduced the speed to 25 clicks per second it worked fine. Unfortunately I had to add extra wires to allow myself to program the chip while it was in the mouse – a major pain that complicated the project more than I wished!

rapidfire_mouse_mod (7)

Here’s a good view of the transistor. Simply put, when the microcontroller sends power to the “base” pin of the 2n2222 transistor, the “collector” is drained through the “emitter”, and the transistor acts like a switch. It’s shorting the pin, just like would happen if you physically pressed the left click mouse button. When the mouse microchip is positive (+5V), it’s “no click”, but when it goes to ground (shorted by the click button), a click is detected. I biased the “base” pin toward ground by connecting it to GND through a high value resistor. This makes sure it doesn’t accidentally fire when it’s not supposed to.

rapidfire_mouse_mod (8)

Here you can clearly see the programmer pins I added. This lets me quickly access the chip and reprogram it if I decide to add/modify functionality.

rapidfire_mouse_mod (9)

When it’s all said and done, it’s surprisingly slick and functional. I’m using it right now to write my blog, and the button isn’t really in the way. I think it’s one of those el-cheapo buttons you get in a pack of 10 from RadioShack, but I would highly recommend eBay as RadioShack is ridiculously overpriced on components.

rapidfire_mouse_mod (10)

There’s the schematic. Grabbing 5v and GND from a usb mouse is trivial. Heck, most of the circuity/code is trivial! Now that I think about it, this represents are really great starter project for anyone interested in microcontrollers.


Use this diagram of the pin functions for reference.

Remember there’s more than one way to skin a cat! For example, if you don’t want to program a microcontroller, a 555 timer is a simple method and there are tutorials out there demonstrating how to do this. I chose a microcontroller because I can precisely control the rate of firing and the duration. If you decide to do something similar, send me photos and I’d be happy to share them on the site! I love doing tangible projects, however silly they are.

And finally, the code!

#define F_CPU 1000000UL	// frequency (20MHz)
#include <avr/io.h>
#include <util/delay.h>

void on(){
	PORTB |= 1 << PB3; //led
	PORTB |= 1 << PB2; //heater
void off(){
	PORTB &= ~( 1 << PB3 );//led
	PORTB &= ~( 1 << PB2 );//heater

void main() {
	DDRB |= (1<<PB3)|(1<<PB2);
	int ticks;

	for (;;) { //FOREVER
		while ((PINB & _BV(PB4))==0) {} // NOT PRESSED, DO NOTHING
		for(ticks=0;ticks<125;ticks++) // CLICK FOR 5 seconds
			} // CLICK TAKES 1/50'th second

Additional Resources

While working to perfect my temperature-controlled manned experimental propagation transmitter (MEPT), I developed the need to accurately measure temperature inside my Styrofoam enclosure (to assess drift) and compare it to external temperature (to assess insulation effects). I accomplished this utilizing the 8 ADC channels of the ATMega48 and used its in-chip USART capabilities to send this data to a PC for logging. I chose the ATMega48 over the ATTiny2313 (which has USART but no ADCs) and the ATTiny44a (which has ADCs but no USART). From when I see, no ATTiny series ATMEL AVR has both! Lucky for me, the ATMega48 is cheap at $2.84 USD. Here’s my basic circuit idea: IMG_4559

EDIT: the SCHEMATIC1 : PAGE1voltage reference diagram is wrong at the bottom involving the zener diode. Reference the picture to the right for the CORRECT way to use such a diode as a voltage reference. (stupid me!)

MULTIPLE SENSORS – Although in this demonstration post I only show a single sensor, it’s possible to easily have 8 sensors in use simultaneously since the ATMega48 has 8 ADC pins, and even more (infinitely) if you want to design a clever way to switch between them.

LM335 Temperature Sensor – selected because it’s pretty cheap (< $1) and quantitative. In other words, every 10mV drop in voltage corresponds to a change of 1ºC. If I wanted to be even cheaper, I would use thermistors (<$0.10) which are more qualitative, but can be calibrated I guess. Notes on power stability - The output of the sensor is measured with the ADC (analog to digital converter) of the microcontroller. The ADC has a 10-bit resolution, so readings are from 0 to 2^10 (1024). AREF and AVCC can be selected as a voltage reference to set what the maximum value (1024) should be. If the ADC value is 1V (for example) and AREF is 1V, the reading will be 1024. If AREF becomes 5V, the reading will be 1024/5. Make sense? If AREF is fluctuating like crazy, the same ADC voltage will be read as differing vales which is not what we want, therefore care should be taken to ensure AREF is ripple-free and constant. Although I did it by adding a few capacitors to the lines of the power supply (not very precise), a better way would be to use a zener diode (perhaps 4.1V?) as a voltage reference.IMG_4575

Here is my circuit. I’m clocking the chip at 9.21MHz which works well for 19200 baud for serial communication. Refer to my other MAX232 posts for a more detailed explanation of how I chose this value. The temperature sensor (blurry) is toward the camera, and the max232 is near the back. Is that an eyelash on the right? Gross!logger

The data is read by a Python script which watches the serial port for data and averages 10 ADC values together to produce a value with one more significant digit. This was my way of overcoming continuously-fluctuating values.

Here you can see me testing the device by placing an ice cube on the temperature sensor. I had to be careful to try to avoid getting water in the electrical connections. I noticed that when I pressed the ice against the sensor firmly, it cooled at a rate different than if I simply left the ice near it.

NOTICE THE PROGRAMMER in the background (slightly blurry). The orange wires connect the AVR programmer to my circuit, and after the final code is completed and loaded onto the microcontroller these orange wires will be cut away.lm335 microcontroller graph annotated

Here is some actual data from the device. The LM335 readout is in Kelvin, such that 3.00V implies 300K = 80ºF = 27ºC (room temperature). The data is smooth until I touch it with the soldering iron (spike), then it gets cool again and I touch it with a cold piece of metal (wimpy dip), then later I put an ice cube on it (bigger dip). Pretty good huh? Remember, 0.01V change = 1ºC change. The bottom of the dip is about 2.8V = 280K = 44ºF = 7ºC. If I left the cube on longer, I imagine it would reach 0ºC (273K, or 2.73V).

For everyone’s reference, here’s the pinout diagram of the ATMega48:atmega48pinout

Finally, the code to record live data:

import socket
import sys
import serial

ser = serial.Serial('COM1', 19200, timeout=1)
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)

data = ser.readline()
while True:
    data = ser.readline()
    print i,data,val
    if i==100:
        print "nSAVING"

and the code to PLOT the data file:

import matplotlib.pyplot as plt
import numpy

def smoothTriangle(data,degree,dropVals=False):
        """performs moving triangle smoothing with a variable degree."""
        """note that if dropVals is False, output length will be identical
        to input length, but with copies of data at the flanking regions"""
        for i in range(degree,len(data)-degree*2):
        if dropVals: return smoothed
        while len(smoothed)<len(data):smoothed.append(smoothed[-1])
        return smooth

print "loading..."

print "converting..."
data=data/1024.0*5 #10-bit resolution, 5V max

print "graphing"

plt.title("ATMega48 LM335 Temperature Sensor")
plt.ylabel("Voltage (V)")
plt.xlabel("Time (5/sec)")

Also, the AVR-GCC code loaded on the ATMega48:

#define F_CPU 9210000UL

#include <avr/io.h>
#include <util/delay.h>

void init_usart(unsigned long);

unsigned int readADC(char times){
	unsigned long avg=0;
	for (char i=0; i<times; i++){
        ADCSRA |= (1<<ADSC); // reset value
        while (ADCSRA & ( 1<<ADSC)) {}; // wait for measurement
	return avg;

int main (void){

    ADMUX = 0b0100101; // AVCC ref on ADC5
    ADCSRA = 0b10000111; //ADC Enable, Manual Trigger, Prescaler 128
	ADCSRB = 0;


		for(char j=0;j<10;j++){
			sendNum(readADC(10)>>6); // shift to offset 10bit 16bit
			send(44); // COMMA
		send(10);send(13); // LINE BREAK

void sendNum(unsigned int num){
		char theIntAsString[7];
		int i;
		sprintf( theIntAsString, "%u", num );
		for (i=0; i < strlen(theIntAsString); i++)

void send (unsigned char c){
		while((UCSR0A & (1<<UDRE0)) == 0) {}
		UDR0 = c;

void init_usart (unsigned long baud)
	//		Baud Generation
	unsigned int UBRR_2x_off;
	unsigned int UBRR_2x_on;
	unsigned long closest_match_2x_off;
	unsigned long closest_match_2x_on;
	unsigned char off_2x_error;
	unsigned char on_2x_error;

	UBRR_2x_off = F_CPU/(16*baud) - 1;
	UBRR_2x_on = F_CPU/(8*baud) - 1;

	closest_match_2x_off = F_CPU/(16*(UBRR_2x_off + 1));
	closest_match_2x_on = F_CPU/(8*(UBRR_2x_on + 1));

	off_2x_error = 255*(closest_match_2x_off/baud - 1);
	if (off_2x_error <0) {off_2x_error *= (-1);}
	on_2x_error = 255*(closest_match_2x_on/baud -1);
	if (on_2x_error <0) {on_2x_error *= (-1);}

	if(baud > F_CPU / 16)
		UBRR0L = 0xff & UBRR_2x_on;
		UBRR0H = 0xff & (UBRR_2x_on>>8);
		UCSR0A |= (1<<U2X0);
	} else {

		if (off_2x_error > on_2x_error)
			UBRR0L = 0xff & UBRR_2x_on;
			UBRR0H = 0xff & (UBRR_2x_on>>8);
			UCSR0A |= (1<<U2X0);
		} else {
			UBRR0L = 0xff & UBRR_2x_off;
			UBRR0H = 0xff & (UBRR_2x_off>>8);
			UCSR0A &= ~(1<<U2X0);
	//	Configuration Registers
	UCSR0B = (0<<RXCIE0) |//We don't want this interrupt
	(0<<TXCIE0) |//We don't want this interrupt
	(0<<UDRIE0) |//We don't want this interrupt
	(1<<RXEN0) |//Enable RX, we wont use it here but it can't hurt
	(1<<TXEN0) |//Enable TX, for Talkin'
	(0<<UCSZ02);//We want 8 data bits so set this low

	UCSR0A |= (0<<U2X0) |//already set up, so don't mess with it
	(0<<MPCM0) ;//We wont need this

	UCSR0C = (0<<UMSEL01) | (0<<UMSEL00) |//We want UART mode
	(0<<UPM01) | (0<<UPM00) |//We want no parity bit
	(0<<USBS0) |//We want only one stop bit
	(1<<UCSZ01) | (1<<UCSZ00) |//We want 8 data bits
	(0<<UCPOL0) ;//This doesn't effect UART mode

UPDATE: A day later I added multiple sensors to the device. I calibrated one of them by putting it in a plastic bag and letting it set in ice water, then I calibrated the rest to that one. You can see as my room temperature slowly falls for the night, the open air sensor (red) drops faster than the insulated one in a Styrofoam box. Also, I did a touch of math to convert voltage to kelvin to Fahrenheit. You can also see spikes where it quickly approached 90+ degrees from the heat of my fingers as I handled the sensor. Cool!3traces

UPDATE: a day and a half later, here’s what the fluctuations look like. Notice the cooling of night, the heating of day, and now (near the end of the graph) the scattered rain causes more rapid fluctuations. Also, although one sensor is in an insulated styrofoam box, it still fluctuates considerably. This measurement system is prepped and ready to go for crystal oven tests!insulated3