Testing the Microchip MCP3421 18-bit ADC

RE: Testing the Microchip MCP3421 18-bit ADC

Andrew J — Tue, 23 Feb 2021 18:10:58 GMT

Thanks Frank - actually, I wanted to pick your brains if you were using the same one - which you are! I was trying to understand how these three methods worked:

[embed:dc8ab71f-3b98-42d9-b0f6-e21e02a0f8e2:3ef06e6b-9b7d-4651-b12d-db8be7f5e991:type=c_cpp&text=uint8_t+MCP342x%3A%3AgeneralCallReset%28void%29]

{

Wire.beginTransmission(0x00);

Wire.write(0x06);

return Wire.endTransmission();

}

uint8_t MCP342x::generalCallLatch(void)

{

Wire.beginTransmission(0x00);

Wire.write(0x04);

return Wire.endTransmission();

}

uint8_t MCP342x::generalCallConversion(void)

{

Wire.beginTransmission(0x00);

Wire.write(0x08);

return Wire.endTransmission();

}

Transmitting to address 0 is a broadcast: i.e. to all devices on the bus. I would assume this code is written on the basis that there is nothing but one or more MCP342X devices on the bus. In each case it follows with a byte which sets the configuration register for the device:

Page 18 of the datasheet

[View:/resized-image/__size/620x108/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-28b4100e-f801-4693-94c3-27b10cbdc423/8308.contentimage_5F00_207418.png:620:108]

So, taking generalCallReset() as an example, it writes 0x06 or 00000110 so sets S0 and G1 (60SPS/14-bits and x2 Gain). S1/S0 are the Sample Rate Selection bits and G1 and G0 are the Gain Selection bits. I'm not sure that makes sense unless the 'default' configuration is meant to be that - all the examples call this method at the start. That doesn't really make sense and neither do the bytes used in the other two methods.

generalCallLatch() sends byte 00000100 (Sets S0 so 60SPS)

generalCallConversion() sends byte 00001000 (Sets S1 so 15SPS)

There's no documentation/comments for these methods so I was wondering what I was misunderstanding. I have no need or intention of broadcasting but I'd still like to understand these methods.

Any ideas?

RE: Testing the Microchip MCP3421 18-bit ADC

Andrew J — Tue, 23 Feb 2021 17:37:38 GMT

Frank, which library did you use?

RE: Testing the Microchip MCP3421 18-bit ADC

navadeepganeshu — Tue, 23 Feb 2021 06:26:18 GMT

Did you put that small ceramic capacitor on the power supply rail from -ve to -ve?

Misplacement or what does it do there?

RE: Testing the Microchip MCP3421 18-bit ADC

Andrew J — Mon, 22 Feb 2021 22:50:51 GMT

I'm waiting for the delivery of a PCB to use a MC3428 - 16-bit delta-sigma ADC. It will be interesting to see how well that turns out. The good thing about the ADC, compared to the DMM, is that you could characterise the INL and DNL errors and calibrate them out in software, at least to a certain extent. Partly it can be done dynamically and partly with a lookup table although the latter isn't great for a memory constrained device like an Arduino of course. I think there's lots of scope for playing with the one soldered on to a DIP adapter? [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-28b4100e-f801-4693-94c3-27b10cbdc423/contentimage_5F00_1.png:16:16]

RE: Testing the Microchip MCP3421 18-bit ADC

DAB — Mon, 22 Feb 2021 20:07:11 GMT

Nice find.

DAB

RE: Testing the Microchip MCP3421 18-bit ADC

genebren — Mon, 22 Feb 2021 15:46:50 GMT

It will interesting to see how the MCP3421 works in your milliohm meter. Good luck!