Smoke/Temperature Controlled Fan

Transcription

1 Smoke/Temperature Controlled Fan 16 October 2006 Application Note DKAN0006A Features Interface smoke detector with ATTiny12 Interface temperature sensor with ATTiny12 A way to drive AC fans using ATTiny12 Introduction The STK500 and AVR Studio was used to initially create the code and run the simulations. This project uses a single set-point temperature sensor and a photodiode/amplifier IC for inputs into the ATTiny12. The ATTiny12 will output high levels to drive one or two solid state relays to turn on the AC fans. The initial use was for an outside wood boiler and attached shed. Based on the size of the shed, the larger AC fans were chosen based on the amount of air that could be moved. Application This application uses a LED and photodiode/amplifier pair as a smoke detector. As long as there is light on the photodiode, the IC will output a high to the ATTiny12. As with any LED/photodiode pair, if something blocks the light, the output will change to a low. When this happens, the ATTiny12 will sense the change on that input pin and then change the output pin to the relays, turning on the AC fans. The temperature sensor has a similar set-up in that when the temperature set point is reached, a high is output to the ATTiny12, which turns on the fans in the same way. There is also an override switch that will bypass the output of the smoke detector and turn the system on. An output from the ATTiny12 will light up a LED to show that the fans are turned on. The temperature sensor in this instance has a 2C hysteresis. It would be an easy alteration to use a dual temperature set point sensor in place of the single set-point. The ATTiny12 will go to Idle mode unless there has been a change on an input at which point it double checks things to make sure that it was not a spurious change. Hardware Overview: Based on the size of the code and the simplicity of the application, the program was written in assembly rather than C. The Atmel STK500 development board was used for the programming and the initial testing of the code. The ATTiny12 was in SCKT3400D1 (blue) on the STK500 with the ISP6PIN to SPROG1 (blue) in place. To run the program on the STK500, be sure to have wires connecting PB0 and PB2 to LEDS on the board. Also be sure to have PB1 and PB4 connected to switches to simulate the smoke detector and the temperature sensor. PB3 can also be attached to a LED on the board as an option. One thing to remember about the STK500 and the LEDS is that a low will turn them on as opposed to a high. So, when the program is run, the LEDS that are connected to PB0 and PB2 will be on. When the Page 1 of 7

2 switches are pressed, the LEDS will turn off until the switch is released. There will be about a one second delay between release of the switch and the turn on of the LED due to a delay loop within the code. To ensure that LED2 is shining on the smoke detector, a right angle socket was mounted for that IC. Standard sockets were used for the remaining ICs. A LM317 was used for the regulator based on ease of adjustment and what was available. The temperature sensor was chosen based on having a high or low output rather than a serial output. The choice of using the high output from the temperature sensor was based more on a power savings and keeping current from flowing by using the pull-up resistor on that I/O line. A power supply was developed on the board to be able to have the AC easily available. There are better ways to supply power to the assembly, one of which is using a straight 5VDC power supply. The outputs of the SSR(s) can be attached to either the AC Return or power side. For safety reasons, the return side was used but either will work. Software Overview: Essentially, the ATTiny12 goes through the initialization and then goes into an Idle mode. If PB1 goes low due to smoke or PB4 goes high due to high temperature, an interrupt will be generated. The code then does a double check of the pins to ensure that there wasn t a spurious change on one of those pins. If either of those inputs are valid, it will turn on PB3 (to show the fan(s) is active) and PB0 (and PB2 if used) to turn on the SSR. That in turn will turn on the fan(s). The ATTiny12 will then go back to an Idle mode until there is a change on one of those pins. In most situations, the temperature will stay higher even when the smoke might be cleared out enough for the smoke detector to reset. INT0 will only trip when there is smoke. Start Initialize Idle NO NO INT0: Turn On Fan(s) & LED INT0 IN T0 PC I0 PCI0 Is PB4 high? YES Is PB1 high? YES Turn off fan(s) & LED Delay Loop Based on Processor speed Enable INT0 & set up counter Figure 1. Software Flowchart Digi-Key Corporation Page 2 of 7

3 Capabilities, Limitations, and Alterations In this application note, two AC fans were used. However, if there is sufficient power available and it is desirable to run DC fans, than there is a limitation. The ATTiny12 is only able to source/sink an absolute maximum of 40mA per pin, with an absolute maximum of 100mA for the chip. If DC fans were incorporated rather than AC fans, the best way would be to connect the output pin(s) to a MOSFET(s) (as shown below) that is capable of supplying the necessary current to the fans. In this way, it is ensured that the amount of current will not be too much for the microcontroller. Conclusion Figure 2. Alternate DC Fan Control This application note is just one example of the many ways that a small AVR can be used. It is a straightforward application that doesn t use many of the resources of the ATTiny12. The example source code can be easily modified for use of one or two fans in independent modes. Also, a dual set-point temperature sensor can be added to the circuitry fairly easily but the code would have to be adjusted to account for that input. Of course, if DC fans are wanted, it is an easy change to a circuit. Appendix A: Example Source Code ********************************************************************* ***** ***** Program turns an AC fan on or off depending on the ***** presence of smoke across an opto sensor. PortB is ***** configured so that there can be a fan for fresh air input ***** and a fan for smoke output. PortB can be changed as ***** shown with comments if PortB2 is not going to be used. ***** *********************************************************************/.include "tn12def.inc".include "macros.inc".dseg.def Temp=r16 ; Temporary register.def Temp2=r17 ; Second Temporary register.def Fan=r18 ; Fan register.def Count1=r19 ; Timer counter 0 first count register.def Count2=r20 ; Timer counter 0 second count register Digi-Key Corporation Page 3 of 7

4 .equ On=1 ; equate On to a logical 1.equ Off=0 ; equate Off to a logical 0.cseg.org $0000 rjmp Reset.org INT0addr rjmp Smoke.org PCI0addr rjmp Change.org OVF0addr rjmp Count ; reset vector ; Smoke detected vector ; Smoke cleared vector ; Timer to be sure that smoke is cleared keeping ; fan running Reset: // ldi Temp,0x0D ; Set PortB data direction for Pin0, Pin2, and ; Pin3 as outputs and the rest inputs ; Comment out if only using one fan ldi Temp,0x09 ; Set PortB data direction for Pin0 and Pin3 as ; outputs and the rest inputs ; Comment out if using two fans out DDRB,Temp // ldi Temp,0x12 ; Use if PortB0 and PortB2 are used for fans ; Comment out if using just one fan ldi Temp,0x16 out PORTB,Temp ldi Temp,0x60 ; Use if PortB0 is used for fan ; Comment out if using just two fans ; Enable PortB Start: out GIMSK,Temp ;as a high ldi Temp,0x00 out MCUCR,Temp ldi Temp,(1<<SE) out MCUCR,Temp ; Enable PortB1 as an interrupt as a low and PortB4 ; Clear MCU Control Register for enabling pull ups ; on inputs, Idle mode for sleep ; Enable the Sleep mode so controller can go into ; Idle mode Idle: sei sleep rjmp Idle ; Enable Global interrupts ; Put controller to sleep ; RETI brings program counter to this line moving ; controller back to idle mode Smoke: setb PORTB,0 setb PORTB,2 setb PORTB,3 ldi Fan,On ldi Temp,0x60 out GIFR,Temp ldi Temp,0x20 out GIMSK,Temp ; Turn on PortB0 pin ; Turn on PortB2 pin. Can be commented ; out if not using second fan ; Turn on PortB3 pin to show fan is on ; Register to show the fan(s) is on. ; Write a logical 1 to General Interrupt Flag Register ; to clear any flags caused by pin changes ; Enable PortB as any pin change triggers an interrupt Digi-Key Corporation Page 4 of 7

5 reti ; Return to idle mode Change: SKBC PINB,4 rjmp Smoke SKBS PINB,1 ; If temperature sensor is cleared check smoke detector ; If set jump to turn on fan(s) in smoke routine ; Double check smoke detector input to ensure that it ; isn't a spurious level change ; If not set, return to idle mode, otherwise skip this line reti ldi Temp, 0x40 out GIMSK,Temp clr Temp out TCNT0,Temp ;Clear Timer Counter 0 ldi Temp,0x01 out TCCR0,Temp ;Reset interrupt mask so that smoke detector is enabled ;Turn on Timer Counter 0 and use clock as timer source Count: ; Delay routine before fan(s) are turned off inc Count1 cpi Count1,0xFF brne Count inc Count2 cpi Count2,0xFF brne Count Clrb PORTB,0 ; Turn off PortB0 ; If Count1 is not equal to hex FF, then go back to start ; of Count routine ; If Count2 is not equal to hex FF, then go back to start ; of Count routine Clrb PORTB,2 ; Turn off PortB2. Can be commented out if not using ; second fan Clrb PortB,3 ; Turn off PortB3 to turn off LED clr Temp out TCCR0,temp ; Turn off Timer Counter 0 ldi Fan,Off ; Register to show the fan(s) is off reti ; Return to idle mode Digi-Key Corporation Page 5 of 7

6 Appendix B: Example Schematic Figure 3. Example Schematic Digi-Key Corporation Page 6 of 7

7 Appendix C: Parts List Part Part Number Board ND IC1 ATTiny12-8PI-ND IC2 LM317TFS-ND IC3 TC622EPA-ND IC4 OPT101P-ND K1, K ND LED ND LED ND TR ND B1 DB101-BPMS-ND R1 110KQBK-ND R2,R3,R4 330QBK-ND C1 P820-ND C2 P5182-ND ACIN ND Sockets (2) AE9841-ND Socket ED58408-ND Fans (2) P12896-ND Finger Guards (4) CR224-ND ACOUT (2) ND Switch CKC5107-ND Disclaimer Digi-Key offers its Technical Assistance and Design Support Services as a convenience to Digi-Key customers. Digi-Key Technical Assistance and Design Support Services personnel strive to provide useful information regarding Digi-Key products. DIGI-KEY DOES NOT GUARANTEE THAT ANY INFORMATION OR RECOMMENDATION PROVIDED IS ACCURATE, COMPLETE, OR CORRECT, AND DIGI-KEY SHALL HAVE NO RESPONSIBILITY OR LIABILITY WHATSOEVER IN CONNECTION WITH ANY INFORMATION OR RECOMMENDATION PROVIDED, OR THE CUSTOMER'S RELIANCE ON SUCH INFORMATION OR RECOMMENDATION. THE CUSTOMER IS SOLELY RESPONSIBLE FOR ANALYZING AND DETERMINING THE APPROPRIATENESS OF ANY INFORMATION OR RECOMMENDATION PROVIDED BY DIGI-KEY TECHNICAL ASSISTANCE AND DESIGN SUPPORT SERVICES PERSONNEL, AND ANY RELIANCE ON SUCH INFORMATION OR RECOMMENDATION IS AT THE CUSTOMER'S SOLE RISK AND DISCRETION. ACCORDINGLY, THE CUSTOMER SHALL RELEASE AND HOLD DIGI-KEY HARMLESS FROM AND AGAINST ANY AND ALL LOSS, LIABILITY, AND DAMAGE INCURRED BY THE CUSTOMER OR ANY THIRD PARTY AS A RESULT OF ANY INFORMATION OR RECOMMENDATION PROVIDED TO THE CUSTOMER OR THE CUSTOMER'S RELIANCE ON SUCH INFORMATION OR RECOMMENDATION. Digi-Key Corporation Page 7 of 7