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PIC 16F87 Based Grill Timer

I love to cook on my gas grill. Usually I light the grill and let it preheat on high for 10 minutes before putting the food on. Unfortunately, a lot of times I'd forget about it and 20 minutes later I'd check on it and find the temperature had climbed into the red zone.

I also cook pizza on the grill in the summer. I use a stone, but if the pizza is too near the left and right edges, it tends to burn. If I rotate the pizza every 3 minutes it evens it out.

I made this timer to remind me to go to the grill and do whatever I have to do. To use it, you turn the slide switch on and click the Time button on top to set the amount of time from 1 to 15 minutes (10 plus 5). Then you click the Run button. After the time is up, it beeps a piezo buzzer and runs a vibrating cell phone type motor 3 times. The set time LEDs blink as an indication to let you know it's timing.

Files

Schematic

gr_tim02.asm for PIC OR gr_tim02.hex already compiled


Miscellaneous Notes

I wanted to be able to put the timer in my pocket so I found a small case to put it in at Baynesville Electronics where I used to live in Towson, MD north of Baltimore. I'm pretty sure it's a Velleman G403 case.

I used the internal PIC RC oscillator. Time isn't critical.

Photos of the circuit board I made for the project: grillbrd.jpg - grillbrd2.jpg. I used surface mount transistors and resistors to save space.

I didn't have room for a battery holder so I just soldered two AAA batteries together and into the circuit. The black electrical tape is to prevent shorts. I've been using the thing for 2 years now with the same batteries.

The motor is a Jameco 256153 but it looks like that's no longer available. Specs say it's 3V 70ma and 11000RPM. Looks like their 256365 would work. Mine soldered directly to the PC board connections, but you could probably hot glue the replacement in place. I've been buying from Jameco for 25 years or so.

The piezo buzzer is a Radio Shack part# 273-074. Note: The photo of the circuit board shows the buzzer mounted onto the board. When I went to mount it in the case that didn't work. I ended up hot gluing the buzzer over a hole in the cae (up near the top switches in the case front) and running wires to the board.

Jeff Thorssell - Remove the brackets in the email address to email: jthorsse[@]mchsi[.]com

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