Wrong resistors values about open_robot_actuator_hardware

[fgrimminger]

Hi Jochen,

I talked to Joshi who designed and manufactured the foot sensor boards for us.
It's true that we use 10k and 20k ohms for the resistors R4 and R5 and that the voltage divider gives a reference voltage of 2.2V.
This is the setup that we have been using and that has worked well for us.

So we are assuming that there is some other problem with your setup.
Did you try to remove the foot/aperture and shine the led light directly onto the light sensor?
You should measure around 3V on the output and the indicator leds should turn red.
When you cover the light sensor you should measure around 0V on the output and the leds should turn green.

Please note that the 2.2V threshold is only used to switch the led indicators on the foot - on the output wire the analog voltage from 0-3V is transmitted to the microcontroller. So you can always choose in software at which voltage you decide to switch from contact to no-contact.

If you don't get enough light onto the sensor with the foot between the light source and the light sensor the opening in the center of the foot might be too small or the sensor and the opening might not be aligned correctly.

We 3d print the foot with an 1,25mm opening and increase it with a drill to around 1,5mm.
Also the sensing area of the light sensor is not exactly in the center of the component.
That's why we have offset the solder pads and center the sensing area on the board with a microscope. (picture below)

I hope this helps - please let us know if you were able to solve this issue.

Best,
Felix

[jochenalt]

Hallo Felix, Danke für die schnelle Antwort!
Actually, in my setup the voltage at the photosensor is around 1V when it gets illuminated. I dont have an issue with it, with the adapted resistor values it is working fine, maybe I got a different batch of the photosensor, but I believe before soldering it users should check the voltage at the sensor to get the divider right.

Placing the sensor exactly in the centre is indeed an issue, and I believe adjusting the position of the sensor on the PCB is probably not the best way of doing that. Instead I use a slightly bigger hole for the PCB (diameter of 10mm) and glue the PCB in a way that the sensor is in the centre.

I also placed a little cone around the aperture to let it react faster.
Best,
Jochen

[fgrimminger]

Hello Jochen,

o.k. - I'm glad to hear that it's working for you.

Good idea - thanks for sharing your modifications.

Best,
Felix