Interfacing modules which are sending PWM signals as output

Lynxmotion Electronics & Software
1

Hi,

I would like to interface the CMPS03 compass module to the SSC-32.

I have tried the following wiring, but I am failing. I have attached the ground and the + from the CMPS03 to - and + of the 4 AD inputs. Also, I have connected the PWM output of the CMPS03 to “D” of the AD inputs.

If I am looking to what I am seeing in Lynxterm there are numbers moving permanently up and down on ALL 4 input channels. I suppose that I have done something stupid here and that either PWM is not the right thing to connect to the inputs or the wiring is wrong.

Any hints would be very much appreciated

Many thanks

iandi

2

Hi Iandi,

I’m not yet familiar with the Davenport compass, but I got these specs:

Voltage - 5v only required
Current - 25mA Typ.
Resolution - 0.1 Degree
Accuracy - 3-4 degrees approx. after calibration
Output 1 - Timing Pulse 1mS to 37mS in 0.1mS increments
Output 2 - I2C Interface, SMBUS compatible, 0-255 and 0-3599
SCL speed up to 1MHz

robot-electronics.co.uk/shop/Compass_CMPS032004.htm

I see I2c and PWM outputs, neither if which can be directly read by the SSC32. What outputs are you connecting? I’m not seeing an analog output.

There are PIC circuits that can convert PWM signals. The PIC on the BASIC Atom could probably be programmed to do I2C (maybe there’s already a canned routine for I2C in it).

I’d like to find a US distributor for Davenport compass.

Alan KM6VV

3

Hi Alan KM6VV,

many thanks for your reply.

I was hoping to simply use the PWM output of the CMPS03 to the AD input of the SSC-32. But I understand following what you are saying that this is impossible.

I was hoping that it would work as the same works with the Robonova controller board (where you can write PWM data to the analog port)…

Many thanks again

iandi

4

I know the Atom PRO can do I2C just fine because I have used it. I haven’t use I2C on the Basic Atom yet, but will be soon. The commands are I2CIN and I2COUT.

Acroname has the Devantec CMPS03 Compass. I purchased a breakout board for the Honeywell compass module from Spark Fun Electronics.

8-Dale

5

This is not possible. The CMPS03 only has PWM and I2C interfaces, and no analog output. There is no way to connect this to the SSC-32 and read the values from the compass. It’s important to be familiar with the various parts you want to use and the methods they have to interface - two parts must be able to use the interface(s) (PWM or I2C in this case) to communicate. You can find this information in datasheets or manuals for each device you want to interface.

8-Dale

6

Hi 8-Dale,

thanks a lot for this explanation. I understand now!! :wink:)

Best wishes

iandi

7

(Sorry to dig up an old thread…)

Actually, with a resistor and a capacitor, you can make the PWM output of the compass module into an analogue voltage. The resistor and capacitor can be used to form a simple low-pass filter (google ‘r-c filter’ or ‘rc network’). The output of the rc network will be the ‘effective’ voltage of the PWM signal.

8

Hi Matt, Iandi,

Yes, you could, but would you want to? Seems you’d have an R/C time constant, which would be logarithmic. That could mess up a bearing!

If the SSC32 is being “managed” by another processor, then I suggest that it might be better to handle it with the supervisory processor.

I know, maybe an I2C interface (hint) will be added to the next SSC32 board design!

Alan KM6VV