andreww

Thanks for the circuit, works well, would you be able to tell me how many turns is needed for a 1/2 inch form......

also to increase the distance between the coils what can be done.....


cheers,

thanks heaps again for your help!!

Russlk

For 1/2 inch diameter coils, transmit 11.8 turns #30, receive 10.7 turns #30. One way to be able to increase the spacing between coils, is to run the oscillator on higher voltage (more power).

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andreww

I've noticed that the 100 ohm resistor connected to the emitter of the tranny is getting quite warm - is this to be expected?

i'm running the circuit on a 12V DC 300mA plug pack......
the resistor is a 0.5w metal film type.....

cheers

Russlk

Power in the 100 ohm resistor is probably around 300 mW so it should be warm, but not painfully hot.

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andreww

it's getting warm enough that i can't hold on to it

would changing it to a 1w help??

cheers

Russlk

Well---- I think the circuit must be operating inefficiently. Let me simulate the circuit and get back to you.

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Russlk

The power in the 100 ohm resistor is about 800 mW, so yes use a 1 watt resistor. Also increase the 10K to 1 megohm for better efficiency.

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andreww

thankyou for your help, i will give those things a try...

cheers