Atom Pro 28 Voltage Reference for AX0~AX3 A/D

Lynxmotion Electronics & Software
1

Hello all,

I am trying to find a way to change the reference voltage for A/D so that I will be able to get better resolution from 3 axis accelerometer, which outputs 1.33v ~ 1.99v each axis.

I was reading Basic Atom (not pro) manual and I noticed that it had the capability of setting AX3 pin as a voltage reference pin by using the parameter AD_RPOS… But I don’t think BAP28 has that capability because there is absolutely no mention of such feature in BAP28 manual.

Maybe I am just blind or not looking for the right keyword… Has anyone successfully managed to change the Vref for BAP28? I am DYING to know!!! Help! :frowning:

James

EDIT:
I found this
forums.basicmicro.net/viewtopic. … 1fbadd1c76
which sugguests a whole lot of nothing. :angry:
No Vref? Very disappointed, especially since I could’ve potentially doubled up the resolution of the sensor, which is a big deal!

EDIT2:
Ok, I thought of a possible solution… I could build an amplifying circuit using Op-Amp, and just boost the 3 analog signal coming from the accelerometer… I’ll leave this option as my last resort. If anyone has a better solution, please share :wink:

2

My guess, is that it won’t be easy to do. I believe that the pin AVcc that goes into the H8/3694 of the Bap28 is what controls the AtoD conversion and that is hardwired on the chip to +5v. It may be possible to try to break that connection on the chip and wire in your own, but I am not sure if that would be a great thing to do.

Kurt

3

Hello Kurt!

I read the H8/3694 datasheet, but I couldn’t find any useful information regards to changing Vref for ADC
I think I will move on with the current resolution I have, and see if an improvement is necessary.
It sure would’ve been nice if I could’ve stepped it down to 2V though, but oh well :slight_smile:

James

4

The A/D hardware on the H8-36XX chips does not have a VRef. The AVcc can’t really be used as a VRef because of it’s very strict requirements(see the electrical specs). So your pbest option is to use an op-amp to adjust the voltage from your sensor to match the 5v range of the A/D hardware on the AtomPro.