Just a FYI, Squirrel mentioned the reset issue because the schematic posted is an older version. You corrected the GND/5V mix up awhile ago.
thanks for the suggestions!!
1. Reset was based on this. http://arduino.cc/en/main/standalone "Start by connecting a 10k ohm pullup resistor to +5V from the RESET pin in order to prevent the chip from resetting itself during normal operation. The RESET pin reboots the chip when pulled down to ground. In later steps we will show you how to add a reset switch that takes advantage of this."
2. I used external pullups as i read, somewhere, internals were not as reliable/accurate and were prone to noise. If this is incorrect it would greatly simplify the circuit.
3. I was worried about the crystal, i ran out of room. IF i have more room, i could consider.
4. I'll admit i didnt really consider draw. I change batteries often and 3 months sounds perfectly acceptable to me. I used this as a guide
http://forums.trossenrobotics.com/tu...-divider-3264/ and checked the measurements with a voltmeter for accuracy.
5. The battery will be physically isolated using a spdt switch attached to the power lead and the board will be completely off when not in use.
6. I will measure this, thank you.
again appreciate all the comments. I almost went to pcb today, but realized I have a few more things to do.
Just a FYI, Squirrel mentioned the reset issue because the schematic posted is an older version. You corrected the GND/5V mix up awhile ago.
oh crud, will post new schematic
Ah, sorry about the RESET comment, I didn't know u corrected it.
For the external pullups, you are right. The lower the impednace, the better. (wrt stability/emc robustness). If i remember correctly, Atmega's internal pullups are somewhat between 35-50K. So yes, they are not accurate.
But this is fine for the switches. I did several designs with Atmegas/ARMs (not this particulat type) and never used pullups for this type of input (internal switch/button). And I never had problems. And remember: your design operates in the most ideal environment: Battery powered, no high frequencies involved, no high currents, no external connections/log wires, shielded by solid aluminum
very very true
Im going to try to fit the pullups and the caps, but might need to drop the pullups to fit the caps. Any recommendation on a cap size assuming i can get it right up next to the chip?
100nF in a 0402 package is just fine and still hand-solderable.
ok i added the caps. Unfortunately mine resistors are all pulldown, so i cant use the internal pullups (well except for the trigger, and i prefer an external on that)
v10. Thank you Dirty Engineer and Squirrel
Last edited by jptheripper; 03-20-2015 at 09:40 PM.