How to control a 12V H Bridge circuit with a 1.5V polarity switching signal voltage?
You don't. You have a battery available to power your motor. You can use the same battery to power the relays and simply use the output from the receiver as a signal. Optocouplers would be ideal for this as the LED inside is polarity sensitive and thus will only work in one direction. You can then use the optocoupler output to switch the relays. Galvanic isolation between the receiver and the motor circuit comes as an extra bonus:




simulate this circuit &ndash; Schematic created using CircuitLab
The circuit above would turn on relay 1 and 2 when activated. A second, identical, circuit would control relay 3 and 4 but the SIGNAL1 and SIGNAL2 wires coming from the receiver would be reversed so it works with current flowing in the other direction.