ADVERTISEMENT
Here is a simple project based on Attiny13a ( which is limited with 1kb flash and 64bytes of SRAM). In this project a simple sensor node is made out of this and collects data from a digital temperature sensor (ds18b20) and the ambient light with an ldr and converted by the ADC(analogue to digital converter) inside the attiny13a.
Wireless sensor in a transparent tic -tac box to measure light/temperature. It takes 10 micro amps when idle and around 7 milli amps when transmitting. It transmits data in every 16 minutes intervals |
All collected data is send to the receiver via wireless link based on 433mhz OOK modules which needs a protocol to send the data (unlike the dedicated wireless chips with built in protocols and error corrections)
The wireless data is captured in a clock with seven segment led display and a serial connector to send the data to a raspberry pi for further processing.
Example data received from the sensor |
data received from the wireless sensor. Top plot is outside temperature and the bottom one is the light intensity |
Attiny13 based wireless sensor prototype |
Currently at the receive end an atmega328p is used and the result is displayed via serial terminal. But this can be converted in to an oled display/lcd display. More on this and uploading the data to a cloud service and doing analysis on a next post.
The idea of this project is to build from scratch (as far as possible) and use minimalist devices to achieve maximum outcome. I didn't choose assembler, but did the firmware in C and takes exactly 1024 bytes.(This can be the next exercise to free up more space). Within this 1024 bytes , the firmware handles the one wire protocol, reading the ADC, power saving routines and a watchdog timer, and a wireless protocol (borrowed from virtual wire with CRC checksum). The code can be further improved to add some more extras. A small pcb is made which can be used for pro-typing alternate projects such as rolling code remote, wireless water tank overflow detection/pump control etc)
Hardware
The prototype is built on a 2 X 3cm pcb , home etched (details below) and has an sop (attiny13) some connectors and ldr, ds18b20, some pull-up resistors.Schematic for the transmitter prototype. The diagram is missing a 10k pull up resistor for the data pin for the one wire thermometer (ds18b20) |
The rf module used is shown below with a simple wire antenna
Firmware
The software and the source can be downloaded from the github here. It needs avr-gcc to compile and use avrdude to upload to the chips using an isp programmer. you may use an arduino uno as an isp programmer. There is a make file and all you need to do is type inmake flash
Building from scratch
1) PCB - can be made using a presensitised board (e.g Bungard) or toner transfer.A simple one side PCB for the prototype board |
All cad files can be downloaded from the project page on github.
A few pictures from my prototype is shown below
step 1) making a layout
PCB layout (step 1) |
Step 2) uv exposure (home made with uv led)
3) Developing (bungard)
4) Etched board (ferric chloride)
5) Applying solder mask
6) Assembling
Firmware (main routine in tx)
#include <avr/io.h> #include <util/delay.h> #include <avr/interrupt.h> #include <string.h> #include "virtualwire.h" #include <avr/sleep.h> #include <avr/wdt.h> #define DS18B20_PIN PB4 #define BUTTON_PIN PB2 // CHANGE IN TX LIBRARY FILE IF CHANGED #define LDRPIN PB3 #define LEDPIN PB1 typedef struct messagedata { unsigned char RX_ID; unsigned int temperature; unsigned int light; unsigned char button; } messagedata; messagedata txdata={.RX_ID='A',.temperature=25,.light='L',.button='L'}; // watchdog interrupt ISR(WDT_vect) { wdt_disable(); // disable watchdog } static void myWatchdogEnable() { cli(); MCUSR = 0; // reset various flags //set timer to 1 sec //WDTCR |= (0<<WDP3) | (1<<WDP2) | (1<<WDP1) | (0<<WDP0); //set timer to 8 sec WDTCR |= (1<<WDP3) | (0<<WDP2) | (0<<WDP1) | (1<<WDP0); WDTCR |= (1<<WDTIE); WDTCR |= (0<<WDE); sei(); wdt_reset(); //call to this reset the timer set_sleep_mode (SLEEP_MODE_PWR_DOWN); sleep_mode(); // now goes to Sleep and waits for the interrupt } int main(void) { DDRB &=~(1<<LDRPIN); //ADC0 is input PB5 uint16_t nticks=37; // number of prescaled ticks needed TRY 150 uint8_t prescaler=2;; // Bit values for CS0[2:0] TRY 1 TCCR0A = 0; TCCR0A = _BV(WGM01); // Turn on CTC mode / Output Compare pins disconnected TCCR0B = 0; TCCR0B = prescaler; // set CS00, CS01, CS02 (other bits not needed) OCR0A = (uint8_t)(nticks); TIMSK0 |= _BV(OCIE0A); vw_ddr |= (1<<vw_tx_pin); vw_port &= ~(1<<vw_tx_pin); uint16_t t; uint8_t rcvdSize = sizeof(txdata); // Set the ADC input to PB3 or ADC3 ADMUX |= (1 << MUX0); ADMUX |= (1 << MUX1); ADMUX |= (1 << ADLAR); ADCSRA |= (1 << ADPS1) | (1 << ADPS0) | (1 << ADEN); sei(); while (1) { t=DS18B20_read(); txdata.temperature=t; //t = adc_read(); ADCSRA |= (1 << ADSC);//start conversion while (ADCSRA & (1 << ADSC)); txdata.light=ADC; uint8_t counter=9; while(counter) { vw_send((uint8_t *)&txdata, rcvdSize); vw_wait_tx(); _delay_ms(500); counter--; } ADCSRA &= ~(1<<ADEN); //turn off ADC ACSR |= _BV(ACD); // disable analog comparator counter=120; while(counter) { myWatchdogEnable (); // 8 seconds counter--; } ADCSRA |= (1<<ADEN); //turn on ADC } }
No comments:
Post a Comment