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I have an existing RC circuit for a toy truck. Obviously it already has its own mC to receive the antenna signal and output a PWM signal to a motor driver IC.

I want to be able to ALSO control this motor driver IC from an ESP8266 but I would like to do so in a non-invasive/non-permanent manner, ie I would want to be able to simply remove my ESP8266 at some time and the RC truck will still be functional as if it was stock.

I would like to only introduce/add an IC that would allow me to choose between which PWM signal to use to drive the motor driver IC.

I would like that if the ESP8266 is not present it use the existing mC PWM signal, ie use the existing mC signal by default and if the ESP8266 is present I can choose from the ESP8266 which PWM signal to send to the motor driver IC.

thanks in advance for your help!

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ If you mean a microcontroller by mC, i think it should be abbreviated as uC. RC means radiocontrolled? \$\endgroup\$ – Huisman Sep 20 at 17:20
  • \$\begingroup\$ Transmission gates or simple pluggable links seems the straightforward solution. \$\endgroup\$ – Andy aka Sep 20 at 17:22
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Use a multiplexer, the cost nothing and are designed for exactly this purpose. Even the schematic tool knows a symbol for them.

If unsure about the function of the MUX add a pulldown (or pullup) resistor to ensure the state if the enable-input is left open.

Don't forget to protect at least the MUX with TVS Diodes from ESD damage, if you intend to disconnect the connection.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Something like the 74LVC1G157 would be a good IC for this, and it probably doesn't need any TVS diodes. \$\endgroup\$ – Caleb Reister Sep 20 at 21:52
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There are many ways to achieve this goal. Possibly one of the simplest is to use a SPDT relay. The relay switch contacts would be connected as follows:

  1. NC terminal to the existing uC PWM output.
  2. NO terminal to the ESP8266 PWM output.
  3. COM terminal to the motor controller PWM input.

The relay coil would be connected to a suitable power source and then driven with an NPN or a N-FET transistor. The transistor would be controlled from the ESP8266 PWM selection signal output.

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  • \$\begingroup\$ Very rugged method. Has some advantages. Can be designed to run with the motor's voltage. \$\endgroup\$ – Ariser Sep 20 at 18:29

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