MSM501-Firmware

Firmware for MSM501-MainsReciprocalCounter.

Overview

This is the firmware for MSM501-Mains Reciprocal Counters.
Find the hardware and documentation in this repository.
This is just an Arduino script you can upload using the official Arduino IDE.
Hardware and software are built around an Arduino Nano.
Measurement results are in uHz and sent out over serial on header J2.
They are sent as ASCII and separated by LF and CR.
Default parameters: 115200 baud, 8 data, 1 stop, no parity
You can use this serial logger to save the output to a file.

Example output

50020548\r\n
50032928\r\n

Configuration

Change the constant defaultGateTime to vary the measurement time (value in ms).
A shorter measurement time lowers effective resolution but increases the update rate.

Change the constant refClockFrequency to the reference clock frequency (in uHz) you are using.
The reference can be supplied externally via BNC (CN2) or from the reference oscillator (X1).

Change the constant correctionOffset to an offset applied to the reference frequency (in uHz).
If you don't know your clock offset, set this value to zero.
See the section "Calibration" of this document for more information on how to determine the offset.

Calibration

1. Remove the link on JMP1 (J3).
2. Apply a calibration frequency to the center pin of J3.
   The calibration frequency must be a 0–5 V square wave.
   Preferably 50 Hz or 60 Hz and a 50% duty cycle.
3. Record the measured frequency of the MSM501.
4. Calculate the offset as follows:
   All values should be entered in uHz.
   Where f_ref is the nominal reference frequency,
   f_cal the applied calibration frequency and f_measured the recorded measurement result.
   $correctionOffset = f_{ref} - (\frac{f_{measured}}{f_{cal}} \times f_{ref})$
5. Enter the offset into the firmware.

Other

Published under GPL-3.0 license.