shivasage
Junior Member level 1
Hello. I'm planning a project which aims to regulate an output voltage from 0 to +5V DC by using a force sensitive resistor. I posted about this a while ago, and some forum members helped me create a schematic. Now I'm back. This is for a musical implementation: I own an effect pedal which accepts 0 to +5V voltage to control certain parameters. Thus, the harder I push on the sensor with my finger, the parameters will change.
Originally I had planned a circuit using an op-amp (moderator action: removed link to external source)...missing some caps). In this schematic, the sensor is represented by the 68k resistor, as it starts at several million ohms with zero pressure and gets down to ~68k ohms with maximum pressure. The 1M resistor represents a pot I will place in the feedback loop to fine-tune the response. The 50k load represents the input of the effect pedal (this value sourced from the owner's manual).
When attempting to breadboard the circuit, the op-amp malfunctioned and I didn't have a replacement. I didn't want to order parts just yet, so I tried coming up with a simpler circuit (moderator action: removed link to external source) to achieve the same thing. In this schematic, the 100k pot controls the incoming voltage to fine-tune the response. The 6.8k resistor in series is to lower the power running through the pot when it is at minimum resistance to avoid damaging the pot (I have since lowered this value to 2k), and the 50k resistor in parallel has a similar effect of allowing the current to flow elsewhere besides through the pot, and it also smoothed out the taper of the output voltage.
My question is: Is there any downside to using the simpler circuit vs. the op-amp circuit? One issue that I'm aware of is that the load will have a significant effect on the output. However, because the load will always be the same (i.e. I'm always going to use the same effect pedal), does this matter? I thought it was weird that there was zero current flowing, but from the manufacturer: "the input is 0-5V, current won’t matter because there’s a >100k input resistor and the current is self regulating and protected." (He says 100k but the manual says 50k, not sure which is right, but could be compensated for with the pot.) He also told me the pedal has overvoltage protection, which alleviates another potential concern.
Originally I had planned a circuit using an op-amp (moderator action: removed link to external source)...missing some caps). In this schematic, the sensor is represented by the 68k resistor, as it starts at several million ohms with zero pressure and gets down to ~68k ohms with maximum pressure. The 1M resistor represents a pot I will place in the feedback loop to fine-tune the response. The 50k load represents the input of the effect pedal (this value sourced from the owner's manual).
When attempting to breadboard the circuit, the op-amp malfunctioned and I didn't have a replacement. I didn't want to order parts just yet, so I tried coming up with a simpler circuit (moderator action: removed link to external source) to achieve the same thing. In this schematic, the 100k pot controls the incoming voltage to fine-tune the response. The 6.8k resistor in series is to lower the power running through the pot when it is at minimum resistance to avoid damaging the pot (I have since lowered this value to 2k), and the 50k resistor in parallel has a similar effect of allowing the current to flow elsewhere besides through the pot, and it also smoothed out the taper of the output voltage.
My question is: Is there any downside to using the simpler circuit vs. the op-amp circuit? One issue that I'm aware of is that the load will have a significant effect on the output. However, because the load will always be the same (i.e. I'm always going to use the same effect pedal), does this matter? I thought it was weird that there was zero current flowing, but from the manufacturer: "the input is 0-5V, current won’t matter because there’s a >100k input resistor and the current is self regulating and protected." (He says 100k but the manual says 50k, not sure which is right, but could be compensated for with the pot.) He also told me the pedal has overvoltage protection, which alleviates another potential concern.
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