Measure capacitance values using the arduino control CN0552 evaluation version

Question

1.I wonder if the CN0552 can be controlled with arduino 
 2.If it can be used, I would like you to send the corresponding program code that I can refer to. 
 3.Can the code of the AD7746 be used for the control of the CN0552 and how?

JoanOrtega · Accepted Answer

Hi Ikxaaa, 
 The provided No-OS drivers are available for the following platforms. If you do not use any of those platforms you will problably need to modify the No-OS drivers: 
 
 In the following link you can see where the pins are connected EVAL-CN0552-PMDZ Overview [Analog Devices Wiki]

I do not understand what you mean with CIN1_POS and CIN1_NEG measurements. One measurement should be the difference between CIN1_POS and CIN1_NEG and the second measurement should be the difference between CIN2_POS and CIN2_NEG. 
 Regards 
 Joan)

MarkThoren · Answer

You might want to break things up into a couple of steps. Here's a similar function for an ADC that has an offset binary format: 
 https://github.com/analogdevicesinc/Linduino/blob/master/LTSketchbook/libraries/LTC24XX_general/LTC24XX_general.cpp#L389 
 I think you need to subtract the 0x800000 offset first, before casting as a float; you're doing this in a single step and I'm not sure what the result will be. 
 (Also it looks like you're subtracting 0x80, not 0x800000). 
 Try making a small test program that only exercises that formula, step through a range of input values, and make sure the output is as expected. That way you can debug this completely independently of the actual part. 
 -Mark

JoanOrtega · Answer

Hi Ikxaaa, 
 The No-OS drivers are a set of functions, registers and parameters that we provide to facilitate the programming of the device (in your case the AD7746) for any microcontroller. The No-OS drivers can be found in: no-OS/drivers/cdc/ad7746 at master &middot; analogdevicesinc/no-OS &middot; GitHub (AD7746.h adn AD7746.c) 
 In you case, I can see that you have generated you own No-Os drivers (AD7746.cpp and AD7746.h) for your Arduino board and we cannot provide any support. 
 Anyway, just having a quick look to your code it seems like it is working, and you are reading properly from your device. The value read indicates that the value measured is out of the range since 16777215 is the maximum allowed value. 
 Regards 
 Joan

MarkThoren · Answer

From the datasheet description of the 24-bit cap data register: 
 The 0x000000 code represents negative full scale (&ndash;4.096 pF), the 0x800000 code represents zero scale (0 pF), and the 0xFFFFFF code represents positive full scale (+4.096 pF). 
 This is offset binary. You can subtract 0x800000 first, which will result in a signed, 2s complement number. Be careful that the sign extension is done properly if you are using a 32-bit word. 
 then multiply the result by the value of one lsb, which would be 4.096 pF / 8388608 
 It is a good idea to double-check your math by passing known values to it, and make sure it returns the expected result. (for example, sending digital code zero, 0x800000, 0xFFFFFF should return -4.096, 0, and 4.096, respectively. 
 -Mark

MarkThoren · Answer

The procedure for calibrating an offset is described on page 23 of the AD7746 datasheet, and it's noted that board level stray capacitances often dominate. 
 Not sure how to explain the subtraction error - although you're mentioning 0x80000, with four zeros, should it be 0x800000 (an 8 with five zeros)? 
 -Mark

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Measure capacitance values using the arduino control CN0552 evaluation version