Am I correct in thinking the following would work...
GPIO pin 40 feeds the LED of optoisolator (standard or darlington?) and the output arrangement is like the attached screen grab,
but with 12v, not 24v, and (in the image) the motor is replaced by a small SPDT relay which is connected to act like the TX/RX switch in the G8ADE
sequencer circuit (CQ-TV 125)
Portsdown 4 sequencer
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Rishtonite
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Portsdown 4 sequencer
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Re: Portsdown 4 sequencer
That circuit is more complicated than necessary and lacking a vital component. A relay is an inductive device and there should be a reverse diode across the coil to dump the back-EMF when switching off.
This is what you should use:
This is what you should use:
Doppler effect: The tendency of stupid ideas to seem smarter when they come at you rapidly.
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Rishtonite
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Re: Portsdown 4 sequencer
Thanks for the comments and new diagram. After posting I did think more about it and realised it wasn't the best solution.
Is "V in" straight from pin 40, no opto ??
Is "V in" straight from pin 40, no opto ??
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radiogareth
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Re: Portsdown 4 sequencer
Yes, that's right, via the 1k resistor. Its what I use for my 'PTT' control, both Portsdown and Langstone have a 100mSec delay after making that pin high before any RF is emitted.
Gareth
Gareth
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Rishtonite
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Re: Portsdown 4 sequencer
Thanks.
Testing my (not fully wired yet, pluto with stubby antennas, no Power amp) system I checked with testcard selected, pressed TX on the Pi screen and it took about 3 seconds for 3.3v to appear on pin 40 of the Pi header.
Unless I've misunderstood the coment about 100mS, from your comments that sounds like it's wrong.
Or maybe the 3 seconds is correct, then it takes another 100mS for Pluto to start TXing?
I'm confused when I look at the functions of other pins. For working 23cm (only) should there be any other header pins taken hi or lo (via a resistor?)
Testing my (not fully wired yet, pluto with stubby antennas, no Power amp) system I checked with testcard selected, pressed TX on the Pi screen and it took about 3 seconds for 3.3v to appear on pin 40 of the Pi header.
Unless I've misunderstood the coment about 100mS, from your comments that sounds like it's wrong.
Or maybe the 3 seconds is correct, then it takes another 100mS for Pluto to start TXing?
I'm confused when I look at the functions of other pins. For working 23cm (only) should there be any other header pins taken hi or lo (via a resistor?)
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radiogareth
- Posts: 1392
- Joined: Wed Jan 06, 2016 9:46 am
Re: Portsdown 4 sequencer
Correct, "Or maybe the 3 seconds is correct, then it takes another 100mS for Pluto to start TXing?"
t takes 3 seconds or so for the Rpi to create and get ready to send the data stream. The RF appears 100mSecs later than the stream is ready. Its working quite hard to do the encoding (even commercial TV takes a couple of seconds).
Other than controlling external things like different amps, filters etc, you don't need any of the other pins except PTT. Later on if you want to build/use some of the test gear, some are needed, but for single band Pluto TX with no amp nothing is needed unless you wish to route the antenna from Pluto to receiver.
Gareth
t takes 3 seconds or so for the Rpi to create and get ready to send the data stream. The RF appears 100mSecs later than the stream is ready. Its working quite hard to do the encoding (even commercial TV takes a couple of seconds).
Other than controlling external things like different amps, filters etc, you don't need any of the other pins except PTT. Later on if you want to build/use some of the test gear, some are needed, but for single band Pluto TX with no amp nothing is needed unless you wish to route the antenna from Pluto to receiver.
Gareth
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Rishtonite
- Posts: 21
- Joined: Tue Jun 03, 2025 4:03 pm
Re: Portsdown 4 sequencer
Many thanks for the useful info.
I'm pleased that the 3 second delay is normal/expected.
I have the PD4, a Pluto and a PicoTuner, coax relay, 15 watt amp. I presume the PTT is for a physical switch?
My plan is to use the TX 'button' on the Pi screen to put it into transmit and use the sequencer to then operate the relay (to switch between the tuner and Pluto/Amp), then apply power to the amp. Obviously reverse that sequence when going back to receive.
The coax relay is SPDT https://thedxshop.com/product/tohtsu-cx ... ial-relay/ with the 'not in use' connector shorted to ground.
I'm pleased that the 3 second delay is normal/expected.
I have the PD4, a Pluto and a PicoTuner, coax relay, 15 watt amp. I presume the PTT is for a physical switch?
My plan is to use the TX 'button' on the Pi screen to put it into transmit and use the sequencer to then operate the relay (to switch between the tuner and Pluto/Amp), then apply power to the amp. Obviously reverse that sequence when going back to receive.
The coax relay is SPDT https://thedxshop.com/product/tohtsu-cx ... ial-relay/ with the 'not in use' connector shorted to ground.
Re: Portsdown 4 sequencer
OK, but that relay needs a fair amount of current to you might want to use a more capable transistor or an intermediate relay. I don't think you need a sequencer. The CX520D has poor isolation on 23cm so be careful. Also, what filter are you planning to use in front of the picotuner? You do need one because there are many strong signals around and the tuner is wideband. A simple 4 post cavity filter would do - see the wiki.
Mike
Mike