Treadmill driver reverse engineering and Arduino fitting

[geshka]

Hello team.
I recovered treadmill driver "Jonson fitness" and control panel with feedback loop. It works quite nice on my lathe with 2HP DC motor  - keeping speed and counteracting load.  The only issue is the control panel from treadmill that looks big and silly mounted on lathe. I am trying to get rid from that panel and retrofit Arduino board.  I found nice solution for MC2100 , however I don't have any schematics my driver.
I am trying to watch signals form control panel to the driver board but there is no ground on the board and I afraid to connect scope to it .  Looking into driver board I noticed that it has topology of the SMPS. There is an isolated part of the driver that is "talking" to control panel.   On the picture - it is divided by blue line, transformer wounds marked as red, plus and minus in black.  What if I will ground that "floating" minus of the isolated part of the driver?

[geshka]

Some update...
I was able to connect local minus (area segregated with blue line) to the mains ground and safely connected scope to it.  Here are  the signals on connector from that area which is going to the control panel.
1. Up  - used for incline/decline. Not interested
2. Down  - used for incline/decline. Not interested
3. Ground
4  Plus 15V
5. PWM signal from control panel to the motor driver  freq. 250 Hz.  Duty width of the signal is something strange , need to be investigated further.
6. No signal
7. No signal
8. Signal from tacho sensor from power board to the control panel
9. Plus 5V   

Regarding PWM from control panel to the driver  - as I mentioned  - quite weird. at this moment what I see is the constant duty cycle about 50%, however during the speed change from control panel it wider or narrower  (depends on requested speed) and then, when speed is established, PWM is getting back to 50%.  Weird...
   

[electro_lex]

Hi Geshka,

 Thanks for posting this info. I have the same board and I want to drive it with a micro controller.

 Did you end up figuring out the PWM control signal on pin 5?
 Does the duty cycle vary the motor speed or is it more complicated than just PWM? What is the PWM signal peak voltage?