Go Down

Topic: Problem with A7105 (Read 798 times) previous topic - next topic



I'm having a strange issue with connecting the A7105 module to Arduino. I've tried with both Due and a clone of Uno and get the same result.

I connect the A7105 SDIO pin to both MISO (direct) and MOSI (via resistor), creating a 3-pin SPI.
VDD goes to 3.3V, GND to GND
SCK to SCK, SCL to pin 10 on Arduino

Result: doesn't work

However, and here's the magic, if I connect a multimeter parallel onto the resistor (which I did without thinking to check I had the correct resistor), the whole show starts working perfectly. I've tried it with resistors from 0 (direct wire) to 22k.

It seems to not meter if the multimeter is on or off, if it has a battery inside or not.
It does, however, matter what function is selected: ohmmeter and circuit continuity functions make the circuit work, voltmeter and ammeter don't make it work.

So, here's my thinking:
-an ohmmeter without power (switched off, no battery) should act as a Megaohm-range resistor, so connecting it in parallel to a 22k resistor should make next to no difference, yet it seems to make the circuit work
-a voltmeter without power should pretty much do the same, yet it doesn't work

What am I missing? I'm lost.

Pls help



In fact, I just worked it out, sort of...

It works, if the resistance between SDIO and MOSI is around 330ohm, and NOT as I found on various web pages between 10k and 22k, so I was looking in a completely wrong range. This explains why it worked with the "circuit tester" function of mutlimeter plugged in parallel. Also, I was wrong about ohmmeter, it's not a megaohm type resistance equivalent, it's actually a very low one.

(The datasheet for A7105 doesn't specify what resistance should go between SDIO and MOSI, and direct connection for 3-wire SPI doesn't work. Can it be that it's actually unit-specific? The following web page gives 22kohm as the value:
http://www.instructables.com/id/Easy-Android-controllable-PC-Interfaceable-Relati/step5/Building-the-Arduino-driven-radio/ - maybe the author meant 220ohm???)

Anyway, on with the project for me after thus hurdle...

Go Up

Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

via Egeo 16
Torino, 10131