Accuracy of 28 X1 without external resonator?
July 26, 2011
In my circuit, I have 2 Picaxe 28X1s. The only suitable external ceramic resonator I have is on the 28 pin project board and I don't want to ruin it by accident during desoldering. I am making my own board for each Picaxe, and need to know how accurate the timing of the Picaxes will be only using the internal resonator. Picaxe A is using 2 PWM channels driving motors on a separate power supply handled by an L293D, all other outputs to drive other ICs, will read 1 ADC channel, 2 digital sensors, and 1 digital input. It will be running a continuous program that runs a robot. Picaxe B just uses 2 PWM outputs to drive LEDs and reads 1 ADC channel.
Since it's controlling a robot, the PWM channels have to be pretty precise since I want the motors to go the correct speeds, and the second Picaxe is modulating a constant 38khz pulse to drive some IR LEDs. PWM is mainly the only thing I'm worried about, and my motors are on a separate power supply.
My questions are:
Most importantly, does only using the internal resonator sound accurate enough for this?
If not, I do have some salvaged 4 MHz 2-pin crystals that look like they're in good shape, and have no damage from soldering heat. If I were to use these instead, what would be the best capacitor values?
Lastly, If I had to resort to removing the resonator from the project board, what would be the best way to remove it without damaging it from heat? I use a medium heat 25 watt, small tipped iron, and only have some desoldering braid to use (and from RadioShack too, so sometimes it doesn't even work).