Mikro Pi ADC Reading All Zeros

Question

I have a Raspberry Pi 2 B with a MikroElektronika Pi Click 3 shield with a Click Force add-on board. I installed Raspbian Stretch and enabled SPI devices. The Pi Click 3 shield has a MCP3204 ADC on it and the Click Force add-on board feeds an analog signal to either channel 1 or 2. There is a dip switch on the Pi Click shield that allows you to bypass the ADC and send the signal directly to one of the Pi's GPIOs. I have verified that the dip switch is set to send the signal to the ADC. I have run the sample code available from MikroElektronika and it outputs all zeros. I also looked up another example and used their code, which wasn't really that different and got the same result. The fact that they are all identically zeros is suspect to me. I'm not sure what to do to problem solve this issue. Any ideas? This is my first Raspberry Pi project, and I thought it was going to be easy going with the MikroElektronika boards, but there is basically no information for these with respect to Raspberry Pis.

cnardin · Accepted Answer

I was able to resolve the issue after contacting Mikroe directly. The solution is rather simple. The Raspberry Pi has two SPI interfaces, but the documentation from Raspberry Pi doesn't mention this. It walks you through how to enable SPI, but it only enables SPI0. So when you are done you would see /dev/spidev0.0 and /dev/spidev0.1. But the ADC on the Pi Click Shield is wired up to SPI1 channel 3, which requires a different method to enable (see Enabling SPI1 on the Raspberry Pi B+/Zero/2/3). All it took was to add the line:

dtoverlay=spi1-3cs,cs0_pin=16

to the end of /boot/config.txt and reboot my pi. After that everything worked perfectly.

As an aside, the support from MikroElektronika was good, but the documentation is sparse at best with respect to Raspberry Pi. The product page has a few links at the bottom, including a couple spec sheets and a link to the sample code. Hopefully this will help some one else in the future.

Cheers!

michaelkellett · Answer

Thanks for posting your solution - so many people don't bother. What are you planning to do with the analogue inputs on your Pi ? MK

shabaz · Answer

The Click board range is really very comprehensive, but as I understand some MikroE stuff is not open source, or documented as well as desired. Unfortunately when documentation gets tough, the only solution is to dig out the chip datasheets, and follow the detail there. This is usually not too bad, but does mean some practice is needed examining chip data. I'm not making excuses for MikroE (and agree with you that sample code from them would help), just suggesting that a usable approach in such circumstances (this also applies to many low-cost boards/modules from China too, and from other vendors too so MikroE are not unique) is to start examining the boards at a hardware level as you have done, and be prepared to write your own libraries. For example, for many of the simpler I2C or SPI devices, I sometimes prefer to write my own libraries, since they can be less bloated by being tailored for my needs. Also by googling the chip number (rather than the Click board name) sometimes source code can be found.

cnardin · Answer

I'm using the force click board, which has a power supply and op-amp for a Force Sensitive Resistor. It routes the output signal to the ADC.

c15jon · Answer

You're absolutely right, Shabaz. But I do think it would massively help if they provided a standard level of basic information for all their sensors - the quality of documentation varies wildly. So yes: I'm writing the low level stuff myself (it's a case of having to!). Thanks for replying.

c15jon · Answer

I am using the Pi 3 Click Shield for a number of sensors for a project at work. I am horrified that, for a company that seems to want to get into the Pi market, they have such woeful data about how to connect the Click boards and make them work. I've had to pull together bits and pieces from different places, I have multiple breadboards chained together so I can probe individual pins to see what's going on. I wrote to them and suggested they get someone to put together a collection of Python libraries but they seem completely uninterested. I've spent a whole week faffing about trying to get the Noise Click working and your post regarding SPI Channel 3 has been a revelation. All I need to do now is to figure out how to use it! Thanks so much for sharing.