Input devices

With this assignment I would like to make a circuit board where you could visualize your heartbeat in a shape of piece of jewellery

Techniques
- eagle
- modela
- soldering

Method
In the first place I followed a circuit board which was found on the internet:

http://suchamagicworld.blogspot.com/2008/04/still-alive-heartbeat-irsensor-report.html

This is the eagle file:
heartrate.sch

The construction consists of a device with to two IR leds; an IRemitter and a IRreceiver in order to measure your heartbeat. This device functions also as an clip-on earring.
As the pulse of your heart rate absorbs more light, the receiver gets less light, so get less signal. The necklace exist of the board with the led diode who converts the signal into visible light.

However this concept turned out to be too much work for one week. So, due to lack of time I followed the advice of Bas to extend my hello world board from the last time.

This is the result in eagle:
sieraad

I extend the hello world board with a photodiode, a voltage regulator, resistor and two pin terminal blocks. So, now the aim is you hold your finger in between the photo diode and the IR LED. This should measure your heartbeat.

Findings:
Eagle
- The LM358 has in the schematic view two pins less than the board view. In order to make these pins visible click on evoke. These extra pins only show up on request. You can place them wherever you want.
- It is really important to position the wires and to check the connection, otherwise the board view won't show a trace. So, I missed a trace and had to solve this conundrum with soldering an external wire.

sierraad

While testing the board I found out it didn't function. Blair, Harris and I troubleshooted the board. We compared my board with the hello lightboard of Harris with the help of a oscilloscope. The black scope on the ground and the red scope to the RX. The Harris' board showed a signal of 5V highest value while the lowest value was 0V. On my board the highest value was 5V and the lowest 2.5V. As while signal of the microsecond (µS) were different. Harris' board showed 100µS my board ±35µS. I'm afraid I have to make a new one! : (
The communication with Blair in Detroit and us in Amsterdam through the videoconferencing system went quite well. ; )

Because I continued with the hello.world board I used a different processor (ATtiny44a) for this assignment than the fab modules suggested. Harris adjusted the program to use the external crystal.
This is the adjusted program:

//
//
// hello.light.44A.c
//
// photo transistor hello-world
//    9600 baud FTDI interface
//
// Neil Gershenfeld
// 10/27/10
//
// (c) Massachusetts Institute of Technology 2010
// Permission granted for experimental and personal use;
// license for commercial sale available from MIT.
//

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

#define output(directions,pin) (directions |= pin) // set port direction for output
#define set(port,pin) (port |= pin) // set port pin
#define clear(port,pin) (port &= (~pin)) // clear port pin
#define pin_test(pins,pin) (pins & pin) // test for port pin
#define bit_test(byte,bit) (byte & (1 << bit)) // test for bit set
#define bit_delay_time 100 // bit delay for 9600 with overhead
#define bit_delay() _delay_us(bit_delay_time) // RS232 bit delay
#define half_bit_delay() _delay_us(bit_delay_time/2) // RS232 half bit delay
#define char_delay() _delay_ms(10) // char delay

#define serial_port PORTA
#define serial_direction DDRA
#define serial_pin_out (1 << PA1)

void put_char(volatile unsigned char *port, unsigned char pin, char txchar) {
   //
   // send character in txchar on port pin
   //    assumes line driver (inverts bits)
   //
   // start bit
   //
   clear(*port,pin);
   bit_delay();
   //
   // unrolled loop to write data bits
   //
   if bit_test(txchar,0)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,1)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,2)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,3)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,4)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,5)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,6)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,7)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   //
   // stop bit
   //
   set(*port,pin);
   bit_delay();
   //
   // char delay
   //
   bit_delay();
   }

int main(void) {
   //
   // main
   //
   static char chr;
   //
   // set clock divider to /1
   //
   CLKPR = (1 << CLKPCE);
   CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
   //
   // initialize output pins
   //
   set(serial_port, serial_pin_out);
   output(serial_direction, serial_pin_out);
   //
   // init A/D
   //
   ADMUX = (0 << REFS1) | (0 << REFS0) // Vcc ref
      | (0 << ADLAR) // right adjust
      | (0 << MUX3) | (0 << MUX2) | (1 << MUX1) | (1 << MUX0); // ADC3
   ADCSRA = (1 << ADEN) // enable
      | (1 << ADPS1) | (1 << ADPS0); // prescaler /128
   //
   // main loop
   //
   while (1) {
      //
      // send framing
      //
      put_char(&serial_port, serial_pin_out, 1);
      char_delay();
      put_char(&serial_port, serial_pin_out, 2);
      char_delay();
      put_char(&serial_port, serial_pin_out, 3);
      char_delay();
      put_char(&serial_port, serial_pin_out, 4);
      char_delay();
      //
      // initiate conversion
      //
      ADCSRA |= (1 << ADSC);
      //
      // wait for completion
      //
      while (ADCSRA & (1 << ADSC))
         ;
      //
      // send result
      //
      chr = ADCL;
      put_char(&serial_port, serial_pin_out, chr);
      char_delay();
      chr = ADCH;
      put_char(&serial_port, serial_pin_out, chr);
      char_delay();
      }
   }