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 Forum index » DIY Hardware and Software » Musical Interfaces
simple FSR schematics ?
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R_Gol



Joined: Oct 17, 2019
Posts: 5
Location: World

PostPosted: Thu Jan 16, 2020 12:49 am    Post subject: simple FSR schematics ? Reply with quote  Mark this post and the followings unread

Hi,
I've got two of the FSR 402 Round Force Sensing Resistor( Adafruit)
and I could not find any simple schematic in order to build a cv generator with change of voltage when pressing (Style of the pressure Points by Make Noise)

is anyone could point me to a schematic making the above ?

Any help will be appreciated!

Many Thanks
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JovianPyx



Joined: Nov 20, 2007
Posts: 1943
Location: West Red Spot, Jupiter
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PostPosted: Thu Jan 16, 2020 10:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Since it's a resistor, there can be several ways to get an electrical signal from it. The datasheet will tell you the maximum current you can draw through it. An extremely simple way to get a signal is to form a voltage divider with it. Pick an upper resistor value that limits current to no more than the maximum allowed at your power supply voltage and connect one end to V+. Connect the other end to one end of the force sensor and ground the other end of the sensor. A voltage will be present at the connection of the R you picked and the force sensor. The voltage will change with pressure on the sensor.

The voltage will not be linear with respect to pressure. There are other ways to use the sensor to get a linearized signal. However, nonlinearity may also be inherent in the sensor design, so it may be tricky to get a truly linear voltage - if that's what you need.

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R_Gol



Joined: Oct 17, 2019
Posts: 5
Location: World

PostPosted: Thu Jan 16, 2020 10:56 am    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
Since it's a resistor, there can be several ways to get an electrical signal from it. The datasheet will tell you the maximum current you can draw through it. An extremely simple way to get a signal is to form a voltage divider with it. Pick an upper resistor value that limits current to no more than the maximum allowed at your power supply voltage and connect one end to V+. Connect the other end to one end of the force sensor and ground the other end of the sensor. A voltage will be present at the connection of the R you picked and the force sensor. The voltage will change with pressure on the sensor.

The voltage will not be linear with respect to pressure. There are other ways to use the sensor to get a linearized signal. However, nonlinearity may also be inherent in the sensor design, so it may be tricky to get a truly linear voltage - if that's what you need.


Thank you! I tried what you say and its working! Smile
I saw in the datasheet of the FSR this schematic(https://imgur.com/a/JlFEACF) that using an op-amp( LM358 or LM324 ) with the resistor.

why to do so and what is the difference from the method you mention?

Thanks
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JovianPyx



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PostPosted: Thu Jan 16, 2020 12:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

That is a method of linearization. The signal out depends on the current in which is directly controlled by the FSR. That circuit is better than the simple voltage divider.

Additionally, the opamp buffers the signal so it is strong enough to drive whatever you need.

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R_Gol



Joined: Oct 17, 2019
Posts: 5
Location: World

PostPosted: Thu Jan 16, 2020 12:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
That is a method of linearization. The signal out depends on the current in which is directly controlled by the FSR. That circuit is better than the simple voltage divider.

Additionally, the opamp buffers the signal so it is strong enough to drive whatever you need.

Great thanks!
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The Peasant



Joined: Nov 13, 2009
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Location: Sunny Alberta
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PostPosted: Tue Jan 21, 2020 1:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

There are a couple of different FSR circuits on this page that work very well:

http://www.electronicpeasant.com/projects/synthbend/synthbend.html

Below is a bare bones basic circuit that outputs 0 - 5 volts.

Take care,
Doug


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