Build a Light Watcher

by Michael Simpson

 

This project can form the basis for many other projects.  It demonstrates the ultra low power sleep mode of the Athena Chip.  I originally built this project to monitor my kitchen cabinets.  When a cabinet door is left open for a period of time a small alarm will alert you that they need to be closed.  It's more of a reminder than alarm.   When the cabinet door is closed the chip goes to sleep and eats less then .1ua of power.

You can use this for drawers, closets, fridge or any where there is a change from dark to light.

 

Components

You will need an Athena,  130ohm speaker,  Photo Cell,  Battery Holder and some sort of PC board.  We used the Athena Carrier #1 board for our PCB.  At the end of the application note I list all the parts and sources.

 

Hookup

Schematic 1

Schematic 1 shows how everything is put together.  I will show you step by step in structiuons using the Athena Carrier 1 PCB.

Note:  That the Athena Chip should be programmed before it is inserted into this circuit as there are no provisions to program it once built.   If you want to experiment with the circuit I recommend you breadboard it.  This way you can tweak the program for your own use.

 

Step 1 You don't want to completely build the Athena Carrier.  Only the 18 pin socket, .1uf, 10uf and 10k Resistors are installed as shown.
Step 2 break of 2 pins from one of the headers included with the Carrier Kit.  Solder them in the location shown. Step 3 Insert the Photo Cell as shown and solder in place.
Step 4 This is probably the most difficult part of the installation.  Solder the 100K resistor to the points shown in this picture.  We are connecting it between port 7 and Vss.
Step 5 Install the speaker as shown.  Its installed between port 0 and port 6.
Step 6 In order to use the 4 cell battery holder you will need to move the positive lead.   Remove it by lifting the small tab with the point of a razor knife and pulling the wire.  Once removed just push the wire in to the position shown.

 

 

The battery holder has a sticky pad on the back.  Peel the backing off and stick the circuit board on as shown.

 

Plug the Athena Chip into the socket and connect the modified power connector to the two pin connector you placed on the board.  Note that the black lead (negative) connects to the outside pin.

 

Program (download it here)

'Light Watcher

const speaker 6
SIGNALRES = 0


dim loncount
dim dcounter
dim beepcounter
dim x
clearall

RCSTA=0
gosub lightoff
configio 0,1,2,3,4,5,6,8,9,10,11,12,13,14
p7irq 3

loop:
   onportgosub 7,lightoff,lightflash
   if loncount=0 then
       gosub alarm
   endif
   if dcounter = 100 then
      goto gotobed
   endif

   goto loop

'-------------------------------------
gotobed:
   sleep
   low speaker
   dcounter=0
   gosub lightoff
   goto loop


'------------------------------------
lightoff:
   setvarb loncount,100
   dcounter = dcounter + 1
   beepcounter=0
   return

'------------------------------------
lightflash:
   loncount = loncount - 1
   pause loncount * 2
   dcounter=0
   signal speaker,6,5 'Click
   return

'------------------------------------
alarm:
   if beepcounter=4 then
      goto beepalarm
   endif

   beepcounter = beepcounter + 1
   for x = 1 to beepcounter * 2
      gosub beepit
   next
   setvarb loncount,100
   return


beepalarm:
   gosub beepit
   onportgoto 7,beepalarmexit,beepalarm
   beepalarmexit:
   beepcounter = 0
   setvarb loncount,100
   return

'------------------------------------
beepit:
   signal speaker,100,50
   signal speaker,200,25
   return


 

Parts

Easy RS232 Driver  

Athena

Athena Carrier 1

Photo Cell

4 Cell Battery Holder

100k Ohm Resistor