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Q&A How to change the polarity of an input using a single switch?

I have an mcu pin and I want to sense a voltage up to 24V to 36V. I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be...

1 answer  ·  posted 1y ago by DeadMouse‭  ·  edited 1y ago by Lorenzo Donati‭

Question microcontroller BJT
#10: Post edited by user avatar Lorenzo Donati‭ · 2023-08-10T11:21:44Z (over 1 year ago)
Retagged.
microcontroller BJT
#9: Post edited by user avatar DeadMouse‭ · 2023-06-15T18:49:10Z (over 1 year ago)
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Image](https://electrical.codidact.com/uploads/htfa4bhwyys0hy3cqgy69kkmmf83)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • Note: voltage below 8.2V is considered as "input is floating".
  • This is the truth table
  • | Selection | Voltage | Floating | Ground |
  • |-----------|---------|----------|--------|
  • |Option 1| LOW | HIGH | HIGH |
  • |Option 2| HIGH | HIGH | LOW |
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Image_alt_text](https://electrical.codidact.com/uploads/zywfk1cabt9it98wr54sw4xfh4ep)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • Note: voltage below 8.2V is considered as "input is floating".
  • This is the truth table.
  • For simplicity we will asume that voltage means +24V DC
  • | Selection | Voltage | Floating | Ground |
  • |-----------|---------|----------|--------|
  • |Option 1| LOW | HIGH | HIGH |
  • |Option 2| HIGH | HIGH | LOW |
#8: Post edited by user avatar DeadMouse‭ · 2023-06-15T18:45:19Z (over 1 year ago)
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Image](https://electrical.codidact.com/uploads/htfa4bhwyys0hy3cqgy69kkmmf83)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • This is the truth table
  • | Selection | Voltage | Floating | Ground |
  • |-----------|---------|----------|--------|
  • |Option 1| LOW | HIGH | HIGH |
  • |Option 2| HIGH | HIGH | LOW |
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Image](https://electrical.codidact.com/uploads/htfa4bhwyys0hy3cqgy69kkmmf83)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • Note: voltage below 8.2V is considered as "input is floating".
  • This is the truth table
  • | Selection | Voltage | Floating | Ground |
  • |-----------|---------|----------|--------|
  • |Option 1| LOW | HIGH | HIGH |
  • |Option 2| HIGH | HIGH | LOW |
#7: Post edited by user avatar DeadMouse‭ · 2023-06-15T18:43:40Z (over 1 year ago)
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Schematic](https://electrical.codidact.com/uploads/weoe2idsb7fecs3wsit3p3d7dqi1)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • This is the truth table
  • | Selection | Voltage | Floating | Ground |
  • |-----------|---------|----------|--------|
  • |Option 1| LOW | HIGH | HIGH |
  • |Option 2| HIGH | HIGH | LOW |
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Image](https://electrical.codidact.com/uploads/htfa4bhwyys0hy3cqgy69kkmmf83)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • This is the truth table
  • | Selection | Voltage | Floating | Ground |
  • |-----------|---------|----------|--------|
  • |Option 1| LOW | HIGH | HIGH |
  • |Option 2| HIGH | HIGH | LOW |
#6: Post edited by user avatar DeadMouse‭ · 2023-06-15T18:40:07Z (over 1 year ago)
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Schematic](https://electrical.codidact.com/uploads/weoe2idsb7fecs3wsit3p3d7dqi1)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Schematic](https://electrical.codidact.com/uploads/weoe2idsb7fecs3wsit3p3d7dqi1)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • This is the truth table
  • | Selection | Voltage | Floating | Ground |
  • |-----------|---------|----------|--------|
  • |Option 1| LOW | HIGH | HIGH |
  • |Option 2| HIGH | HIGH | LOW |
#5: Post edited by user avatar DeadMouse‭ · 2023-06-15T18:36:55Z (over 1 year ago)
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • https://i.imgur.com/nCW7NuQ.png
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • ![Schematic](https://electrical.codidact.com/uploads/weoe2idsb7fecs3wsit3p3d7dqi1)
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
#4: Post edited by user avatar DeadMouse‭ · 2023-06-15T17:06:02Z (over 1 year ago)
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Anyway, to be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • https://i.imgur.com/nCW7NuQ.png
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Example below:
  • To be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • https://i.imgur.com/nCW7NuQ.png
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
#3: Post edited by user avatar DeadMouse‭ · 2023-06-15T17:05:31Z (over 1 year ago)
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail).
  • Anyway, to be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • https://i.imgur.com/nCW7NuQ.png
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail). For this reason, I want to provide some selections like switches or jumpers to give the ability in the circuit to be modified.
  • Anyway, to be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • https://i.imgur.com/nCW7NuQ.png
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
#2: Post edited by user avatar DeadMouse‭ · 2023-06-15T17:02:40Z (over 1 year ago)
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • This can be done with a simple NPN.
  • https://i.imgur.com/nCW7NuQ.png
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
  • I have an mcu pin and I want to sense a voltage up to 24V to 36V.
  • I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be open collector outputs.
  • Also, some outputs will be just relays and the other terminal will be at GND or just at the main voltage (supply rail).
  • Anyway, to be able to connect an mcu to a high voltage I'm using a simple level translator.
  • This can be done with a simple NPN.
  • https://i.imgur.com/nCW7NuQ.png
  • This circuit gives me the following output:
  • LOW: For any voltage above 8.2V
  • HIGH: When the line is floating or when the line is grounded.
  • I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:
  • LOW: When the line is grounded.
  • HIGH: For any voltage above 8.2V or when the line is floating.
#1: Initial revision by user avatar DeadMouse‭ · 2023-06-15T16:59:42Z (over 1 year ago) 
How to change the polarity of an input using a single switch?
I have an mcu pin and I want to sense a voltage up to 24V to 36V.

This can be done with a simple NPN.

https://i.imgur.com/nCW7NuQ.png

This circuit gives me the following output:

LOW: For any voltage above 8.2V  
HIGH: When the line is floating or when the line is grounded.

I want to add a switch or a jumper to modify this circuit on the fly and change its behaviour as following:  

LOW: When the line is grounded.  
HIGH: For any voltage above 8.2V or when the line is floating.