fsr circuit design feedback

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The Peasant
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Re: fsr circuit design feedback

Post by The Peasant » Thu Jan 14, 2021 1:29 pm

Right. Those resistors determine the maximum current that can flow through the FSR.

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Re: fsr circuit design feedback

Post by ketem13 » Thu Jan 14, 2021 1:39 pm

The Peasant wrote:
Thu Jan 14, 2021 1:29 pm
Right. Those resistors determine the maximum current that can flow through the FSR.

Take care,
Doug
Thank you! I will make them 10k to be at the safe side..

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Re: fsr circuit design feedback

Post by guest » Thu Jan 14, 2021 7:44 pm

ketem13 wrote:
Thu Jan 14, 2021 10:49 am
any other cmos I can use instead of the 4013?
of course I will have many other cmos but not the one I needed... :despair:
what other cmos do you have? you can make it with a schmitt trigger (which could be made out of opamps as well), or with J/K flip flops, or NOR gates. anything that latches and holds state.
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Re: fsr circuit design feedback

Post by ketem13 » Fri Jan 15, 2021 3:25 am

guest wrote:
Thu Jan 14, 2021 7:44 pm
ketem13 wrote:
Thu Jan 14, 2021 10:49 am
any other cmos I can use instead of the 4013?
of course I will have many other cmos but not the one I needed... :despair:
what other cmos do you have? you can make it with a schmitt trigger (which could be made out of opamps as well), or with J/K flip flops, or NOR gates. anything that latches and holds state.
I do have in hand: 40106,4069,4066,4093,4070,4052,4017,4051,4024,4040,4046

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Re: fsr circuit design feedback

Post by guest » Fri Jan 15, 2021 4:14 am

how about something like this:

http://falstad.com/circuit/circuitjs.ht ... CgCTwdLQgA

the input on the left is from the opamp comparators, and the input on the right is from all the other latch outputs (seperate diode from each). pot goes to an inverting opamp mixer, followed by another inverter to get the polarity right.
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Re: fsr circuit design feedback

Post by ketem13 » Fri Jan 15, 2021 5:02 am

guest wrote:
Fri Jan 15, 2021 4:14 am
how about something like this:

http://falstad.com/circuit/circuitjs.ht ... CgCTwdLQgA

the input on the left is from the opamp comparators, and the input on the right is from all the other latch outputs (seperate diode from each). pot goes to an inverting opamp mixer, followed by another inverter to get the polarity right.
this is what I came with for the moment :
fsr 3.jpg
so my goal is to duplicate the circuit above 3 time then using the latching system you offer.
If I get it right I will need to duplicate your circuit three time and connect my gate output to the left input (represent by the 40hz square wave?) and connect my tuned cv output to the right-hand input in your circuit? I might got confused.. :doh:

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Re: fsr circuit design feedback

Post by guest » Fri Jan 15, 2021 5:23 am

starting with that is fine. all those diodes and transistors will cause offset issues, but will be a great starting point.
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Re: fsr circuit design feedback

Post by ketem13 » Fri Jan 15, 2021 6:37 am

guest wrote:
Fri Jan 15, 2021 5:23 am
starting with that is fine. all those diodes and transistors will cause offset issues, but will be a great starting point.
Sorry for asking again but I think I'm missing something out.
What should be the left hand input in your circuit and what should be the input in the right hand input in your circuit?

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Re: fsr circuit design feedback

Post by guest » Fri Jan 15, 2021 7:14 am

left hand is output of the opamp (before your diode, etc), and the right hand is the output of the other 2 schmitt trigger ciruits (each with their own diode).
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Re: fsr circuit design feedback

Post by johnstilton » Fri Jan 15, 2021 3:32 pm

The Peasant wrote:
Thu Jan 14, 2021 12:51 pm
Current through the FSR is limited by the two 6K8 resistors in series, with 12 volts/13K6 ohms = 0.88mA. Probably safe but if you are using 15 volts then the resistor values should be increased.

There is a bit more circuit detail here:

https://www.sparkfun.com/datasheets/Sen ... rguide.pdf

Take care,
Doug
Doug, will the design you have for the single FSR on your SynthBend build with gates and triggers work on a +/-12V supply with the same resistor values? I want to use your design to provide aftertouch CV on a DIY keybed as you did.

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Re: fsr circuit design feedback

Post by The Peasant » Fri Jan 15, 2021 4:24 pm

Hi John,

Although I haven't tried it, the circuit should work fine on +/-12 volts. You may want to tweak a couple of resistor values, slightly increasing the 33k on the LIN/LOG switch and decreasing the 100k connected between the sensitivity pot and +12V, just to keep the voltages at those points the same as before. You may also want to adjust a resistor value in the trigger output stages if the triggers get a bit too small.

The keybed that was used in the synthbend controller is fairly small and light, so I was able to get good results with one FSR on each end, supporting the front of the keybed. If you are using a larger keybed it may be necessary to use three or more FSRs along it's length, all wired in parallel. If the keybed is significantly heavy, for best results you may want to add some springs to help support some of it's weight.

Just as a side comment, the aftertouch CV on the SynthBend works very, very well and I consider it an indispensable part of the controller. I highly recommend it for any type of synth controller, keyboard, ribbon, or otherwise!

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Doug
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Re: fsr circuit design feedback

Post by ketem13 » Sat Jan 16, 2021 5:00 am

guest wrote:
Fri Jan 15, 2021 7:14 am
left hand is output of the opamp (before your diode, etc), and the right hand is the output of the other 2 schmitt trigger ciruits (each with their own diode).
So I made your latching circuit you ofer in order to check it with two momantery switches and two potentiomers wired from the +12V through the middle lug to the 4066 I/O pin. for the moment it is working great! thank you so much.
I was wandering that if I would like my constant cv to be polarized I will need two use two opamp in attenuverter configuration before entering the 4066 input pin, right?

then I should mix all outputs of the 4066 to one unity gain buffer opamp? or if I will buffer all the constant cv before entering the 4066 ic I will not need to buffer them again ?

Thanks

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Re: fsr circuit design feedback

Post by ketem13 » Sat Jan 16, 2021 6:24 am

Hi again,
So I try that idea using 3 switching and I encounter some issue..
I hope I will manage to explain myself clear as possible. Here is the schematic:
4066 40106.jpg
The upper part marked in green is the 4066 analogue switch that should be turn on or off based on which fsr (in this example momentary switch) is last pressed.

When I try the above schematic with only section one and two it was working great. The moment I added another momentary switch all above stopped to work.

lets say I press momentary switch 1 - it will send a high signal to switch 1 that will turn the first 4066(A) on and at the same time it will send a signal to reset 2 & reset 3 to make their corresponding 4066 switch off(B & C). So ideally when I pressed momentary switch 1 it will turn 4066 A on and will turn off 4066 B and 4066 C

same should happen when I pressed momentary switch 2 - It should switch on 4066 B and at the same time switch off 4066 A and 4066 C.

What mistake I made ? is it type of feedback between the switches that cancelling each other?

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Re: fsr circuit design feedback

Post by guest » Sat Jan 16, 2021 7:16 am

yes, if you want to flip the polarity, then an attenvuerter will work well, or a switch.

they should all be mixed into an inverting opamp.
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Re: fsr circuit design feedback

Post by guest » Sat Jan 16, 2021 7:22 am

what happens if you just put the pots on the 40106 outputs and dont use the 4066?
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Re: fsr circuit design feedback

Post by guest » Sat Jan 16, 2021 7:23 am

also, reset should come from the output of the 40106 not the opamp.
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Re: fsr circuit design feedback

Post by ketem13 » Sat Jan 16, 2021 8:25 am

guest wrote:
Sat Jan 16, 2021 7:22 am
what happens if you just put the pots on the 40106 outputs and dont use the 4066?
it is working as well so I guess no need for the 4066

guest wrote:
Sat Jan 16, 2021 7:23 am
also, reset should come from the output of the 40106 not the opamp.
I think I dont get the routing. When make it with only two switches it seems to work great: link

but when adding another switch it seems I create a feedback that make it not work.. link

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Re: fsr circuit design feedback

Post by guest » Sat Jan 16, 2021 8:35 am

you need a seperate diode from each output to the reset point.
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Re: fsr circuit design feedback

Post by ketem13 » Sat Jan 16, 2021 8:52 am

guest wrote:
Sat Jan 16, 2021 8:35 am
you need a seperate diode from each output to the reset point.
So exiting this is working! thank you very much!

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Re: fsr circuit design feedback

Post by guest » Sat Jan 16, 2021 9:45 am

excellent!
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Re: fsr circuit design feedback

Post by ketem13 » Sat Jan 16, 2021 9:49 am

So while working on falstad very good, it didn't work on breadboard..

is it maybe a wiring mistake? if is it working on falstad it should work the same on breadboard (assuming wiring correctly)

edit:
this is the way I wire it(I hope picture is clear enough):
switch latch 40106.jpg

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Re: fsr circuit design feedback

Post by guest » Sat Jan 16, 2021 10:21 pm

what was the failure mode? did you use switches as you have drawn, or were those replaced with the comparators?
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Re: fsr circuit design feedback

Post by ketem13 » Sun Jan 17, 2021 2:41 am

guest wrote:
Sat Jan 16, 2021 10:21 pm
what was the failure mode? did you use switches as you have drawn, or were those replaced with the comparators?
I use switches exactly like I drawn.

When in that configuration I turn on the power and monitor the first output of the upper potentiometer lug 2. When I press is switch the voltage go up from zero to whenever pot is set. all good. When I try to push either of the other switches the voltage of the first switch is not go to zero and when I monitor theirs corresponding outputs the voltage stay at few mV and not go up as expected.

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Re: fsr circuit design feedback

Post by guest » Sun Jan 17, 2021 5:23 am

you need pulldown resistors on thos diodes
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Re: fsr circuit design feedback

Post by ketem13 » Sun Jan 17, 2021 5:50 am

guest wrote:
Sun Jan 17, 2021 5:23 am
you need pulldown resistors on thos diodes
on their cathode side right? I did put 100K (forgot to drew in the schematic). Still doesn't work

edit: schematic:
40106 latch switch 2.jpg
Last edited by ketem13 on Sun Jan 17, 2021 6:00 am, edited 1 time in total.

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