Will this circuit work

granddad said:

?

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aCtive low

Here is another solution that will probably be rejected like all those already provided. This is based on the assumption that the HC-12 will be only be powered on for a low percentage of the time. A small 3 pole relay would isolate the power and the TX and RX lines. Although it would take more power than an purely electronic solution it may not matter due to the very low duty cycle. It would still need a resistor, a diode and a transistor or mosfet so it may also exceed the OP's maximum component count. Does anyone know if the HC-12 is legal in the UK as it is rated a 100 mW output at 433 MHZ ?

Les.

granddad said:

Taken...( My post #54) In my book an input tied to a transistor base is ' floating ' it has no driver.... , ( given no bias resistors ) it is just as easy to set an IO pin, LAT =1 and then TRIS as an output , with no opportunity of losing control

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You've already 'lost control', unless you add something to pull the input pin high while it's still an input.

Nigel Goodwin said:

unless you add something to pull the input pin high while it's still an input.

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You mean like R4 and R9 ( post #44)

Yes, I agree with the last design. i guess it will work fine.

You are using a loopback circuit, much like Ford Motor Company did with their Duraspark ignition modules many years ago. If the ground loop remains open, will the transistor tolerate the open circuit?

spec said:

Hi lew,

This is the best bet for switching shield power lines from a controller. It provides isolation between the controller positive supply line and the shield supply positive line so that the shield positive line can be any voltage you like within reason. Of course, the circuit can be scaled for higher voltages/currents if required. The circuit also gives a very low voltage drop between the shield power supply + line and the shield + supply line.

spec

View attachment 98525​

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Hi,

spec said:

Hi lew,

This is the best bet for switching shield power lines from a controller. It provides isolation between the controller positive supply line and the shield supply positive line so that the shield positive line can be any voltage you like within reason. Of course, the circuit can be scaled for higher voltages/currents if required. The circuit also gives a very low voltage drop between the shield power supply + line and the shield + supply line.

spec

View attachment 98525​

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hi spec,
I made this exact circuit. It doesn’t work. The current to HC12 max out at 15.5mA..if I were to power the hc12 directly from my minipro VCC’s pin, it will work and I can see the current spike >20mA during transmission.. it’s like the pnp transistor don’t have enough current to power the hc12..what do u think?

Syafiqridzuan said:

Hi,

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This thread stopped over 3.5 years ago. If you have a similar question, you should start your own thread.

You can include a link to this old thread in your first post as a way of describing your question.

ak

hi ak,

noted. will do. tq