View attachment 239215

Ah! Thank you so much sghioto. What I was trying and failing each time to come up with myself. I will try this over the weekend and feed back the result.

Thank you very much to all of you who have contributed. I very much appreciate your thoughts and time on this.

 

What's wrong with cowboys?

Nothing wrong with regular cowboys, just the type who botch it and scarper.

 

Hi there,

So sghioto's circuit works very nicely at switching between the two coloured LEDs cleanly. I'm not sure if this makes any difference to the circuit but the LED colours are the reverse of what sghioto had in their diagram, so the blue LED (normally on until PTT depressed) is on the 8V rail.

I calculated a 150R resistor would suit the red LED and 270R for the blue LED. With the 8V blue LED lit the (red off) I measure about 5.75V across R3 (150R), which means the resistor (0.25W) is dissipating almost 220mW and close to tolerance. Naturally the 150R resistor gets hot so I was thinking: is the solution to simply use a 0.5W 150R resistor or is there something else I can do to the circuit arrangement to reduce the stress on the 150R resistor?

 

Are you sure about the LED colors. I made a modification shortly after posting the original schematic.
The mod shows the blue LED normally ON connected to the 6.25 supply. The 8 volts from the PTT turns the red ON and should shut the blue OFF.
See post 18.

 

Hi, Ah. I didn't receive an notification that you had updated your schematic. I built the circuit using your original with NPN 2N3904 and that is what I have fed back on.

Sorry, perhaps I should have been clearer in answer to your question in post 8. Perhaps a clearer answer would have been: Yes and that voltage is the 8V rail, i.e. 8V is switched OFF during transmit and switched ON during receive.

In post 13, I thought you were pointing out my switch symbol showing the default state was open circuit, which was incorrect as I assumed you were correctly pointing out. The default momentary switch state while the PTT switch is NOT depressed, i.e. not transmitting, is ON.

Hopefully that clears up any confusion - sorry about that.

In answer to your last queston: Yes, definitely the blue is shown on my schematic on the 8V rail and is always on when the PTT is not depressed. Blue indicates Rx and red indicated Tx. The red LED is on the 6.25V side and the blue LED is on the 8V side. If there is/was something confusing on my schematic please feel free to point it out.

I have corrected the momentary switch state to show it is on by default on my original schematic if this helps.



With all of the above hopefully clarified now will your schematic need to be changed?

Thanks for your engagement on this - much apreciated.

 

Simply reverse the LED colors

 

Okay, thank you sghioto. I will try this tomorrow and feed back. Thank you for you help.

 

Hi sghioto, I tried your new circuit and it works perfectly - thank you very much.

Just a couple of questions, if I may: Within what voltage range could each side (6.25V and 8V) be varied by and the circuit still work at switching between the two LEDs? I can't change either voltage but I was thinking of using the circuit again for a different experimental LED project. Also, I used a 1N4148 for the diode as the forward/reverse voltages and current appear small enough for a 1N4148 to handle - I don't need to use a 1N400-type silicon diode do I?

 

The 1N4148 is fine you don't need the 1N4000 type.
The high side voltage needs to be a minimum of .7volt higher using a 1N4148.

 

Got it. Thank you again for a great solution to my OP request.