Phototrannie to Pot circuit.

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Noumenon

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Hi, I'm rebuilding a MIDI pedalboard a bit.
The board has two volume pedals I want to get rid off and replace with jacks so I can place the volume pedals I want there when/if I need them.

The built in pedals are using a phototransistor circuit and the pedals I want to use does it with a regular potentiometer.

This is the schematic and my idea on it:
**broken link removed**

Red gets 5V. And BICE gets the samething in my mod.
The ideas I have is the one drawn here or by just placing the pot infront of the LED. The best thing would be to replace the whole circuit with one pot, however I doubt that'll work.

Any ideas?
 
I guess you'll have to look better into the original design. How it's done with a phototransistor (I mean, the mechanical part. What's the diode doing and what's the phototransistor doing. How one influences the other one)? What's B1 and B2?

Could you specify those?
 
If you really want to use a pot, I would connect a 20k pot between R and B2 with the slider connected to B1.

Len
 

Just a "toned" plastic filter that moves between the LED and phototran.
R, B1, B2 is the three connections to the circuit.
 
ljcox said:
If you really want to use a pot, I would connect a 20k pot between R and B2 with the slider connected to B1.

Len
Click to expand...

Well, that wouldn't give 10k between R and B2?
Besides, the values has to be the same, but controlled with either a 25k or 250k pot.
 
No, there would be 20k between R and B2.

A 25k pot would suffice.

I am suggesting that the only component is the pot. No resistors, transistors, etc.

Len
 
The reason they use the photo-transistor is because it does not introduce any static into the circuit..
B1 is your output..
B2 is ground..
so B1 is changing between ground and 5V depending on the amount of light hitting the phototransistor..
the origional is actually an elegant little circuit ..
 
ljcox said:
No, there would be 20k between R and B2.

A 25k pot would suffice.

I am suggesting that the only component is the pot. No resistors, transistors, etc.

Len
Click to expand...

Ok, I'll try it and see what the result will be.
 
Noumenon said:
Ok...
So could I then install the pot between B1 and B2 ?
Click to expand...
The origional circuit was designed to supply 5/10000=1/2 a milli Amp over the the entire range from 0 to 5 Volts. i am not sure ,just a pot ,can do that..
How are you going control the volume if you replace the pedals with jacks anyway?
 
I'll plug in pedals that has a 25k or 250k potentiometer in them.
But it's not controlling volume, shure, it's volume pedals (rather expression pedals), but they are connected to a MIDI circuit that transform the difference in values to MIDI data.

And the traditional way is using potentiometers instead of this circuit.
 
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