Problem with Rotary Switch grounding pins - please help.

Thread Starter

gibsoma

Joined Jun 1, 2020
4
HI,
Firstly I am sorry that my electronics knowledge is pathetic, I have tried reading as much as I can to help myself but I am not getting any luck. So I am hoping someone with more knowledge can help me.

I need a rotary switch to select one of nine tracks on an SD card. So position 1 will play file 1, etc up to 9 files. The board I am using is a ys-m3 v7.6, which has 9 analogue pins that activate a corresponding track when grounded. Simple, when using the breadboard and just grounding the pins but when I insert the rotary switch I doesn't work. I have attached an image of what I mean and how I have wired it (RotarySwitch1). When I turn to position 1 on switch then File001 plays as it should. When I go to position 2 then nothing, but when I move on to position 3 then File002 plays. I have tried both "make before break" and "break before make" switches. If I insert a momentary switch into the design and move switch to position and press the switch then the correct files plays (RorarySwitch2) but I don't want to add a button if I can help it.
It seems to simply want a pulse to ground to work correctly whereas when the switch is in position it is permanently connected to ground. However when I move off to another position it plays the track it should have. I am thinking that this breaks the grounding and hence activates the file.
Would anybody have any advice on how to achieve what I need. Sorry again for my primary school understanding of circuits.
 

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ElectricSpidey

Joined Dec 2, 2017
1,156
Quick and dirty solution would be a switch with double the positions you need and turn two positions to change tracks. (one empty position in between each)
You could also try using caps to provide a "pulse".
 

Thread Starter

gibsoma

Joined Jun 1, 2020
4
Thanks Electricspidey for the reply. I am by no means against a "quick and dirty" solution. Its just that this is going to be used by others and turning the switch twice might confuse them. I am interested in the capacitor idea, but again my knowledge lets me down. Would you have any suggestions on how I could use a cap to send the 'pulse'?
 

ElectricSpidey

Joined Dec 2, 2017
1,156
Place a small value capacitor in series with each position, then place a very high value resistor across each cap to discharge it when you select another position so it will be ready again.

I can't really say what values to use because I don't know the input impedance of the device or how long a pulse must be, but I would start with about .1uf and 10 meg ohms.

And use the "break before make" switch.
 

Thread Starter

gibsoma

Joined Jun 1, 2020
4
Thanks ElectricSpidey and KeithWalker, I will give that a go. Keith, I did check the switch with a meter on connectivity and the switched worked as it should. ie. I got connectivity when the number was selected.
 

KeithWalker

Joined Jul 10, 2017
895
If the inputs need a short pulse to ground, use this circuit. Start with resistors = 10 Kohm, capacitors = 0.1uF. If that doesn't work, increase the values until it does.
Keith.
switch.jpg
 
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