Adding external relay control two V2/V3
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EXTERNAL RELAY OUTPUT CONTROL FOR SBITX VERSION 2/3
Goal:? ?to be able to key an external device, such as a linear amplifier, or transverter or similar.?? Rationale:? ?My SB-200 vacuum tube amplifier actually cleans up the signal from the exciter.? ?Since the capabilities of the amplifier are much greater than the sBitx can drive, there is no need for ALC (automatic level control) from the amplifier back to the sBitx.? ? Circuit operation:? ?It is important NOT to expose the sBitx amplifier power lines (+V) to potential feedback or spurious signals, since no "ground" system is perfect, no capacitor RF bypassing can be perfect, and extraneous signals added to the pre-driver, driver or final power lines may show up in the output.? ? Therefore, the output control is? (a) driven by a digital output (TX signal) from the raspberry pi, buffered via the non-conducting gate of a 2N7000 MOSFET, rather than being driven by a switched analog power line (b) isolated from outside signals in its output, by using an optical isolation (PC817)? Mechanical mounting:? ?I used a small breakout board available in quantity from Amazon:??? ?This is not required and others may simply use the PC817 device on their own board.? ?However, I was able to remove the screw terminal connectors to reduce the overall height of this breakout board (may not be necessary actually) and then rewire it to work from 5 volts instead of 12V.? ?The board includes 2 drilled mounting holes.? ?I was able to use standoffs to mount the board? on the right side panel of the sBitx V2 in the space between the raspberry pi and the front panel encoder board.? ? There was adequate clearance.?? Schematic:? ?See attached.? ?changed the series LED resistor to 200 ohms to allow operation on 5 V, interposed the 2N7000, providing a gate protection resistor of 100K.? ?With the board mounted so the LED faces the outside, this provides a nice LED red output to show when the sBitx is in TRANSMIT, a feature that I like.? ? Connections:? ?+5VDC was tapped by soldering to D2 zener protection diode; Ground was obtained from pin 7 of the 74LS08; the TX signal (via RG174 coax ) from pin 2 of the 74LS08.? ?It might be safer to solder a 1Kohm resistor vertically from pin 2 of the 74LS08 and then connect the tiny coax to that to limit current draw from the 74LS08 if there is a short somewhere.? ?? The "Current Transfer Ratio" of the PC817 is not very impressive, 50% - 600%.? ?The current in the LED side is only approx 10mA? ?Therefore, depending on your particular PC817 optoisolator, this circuit may be able to switch anywhere from 5mA to approx 30mA.? ?(Not much current!)? However, the popular optoisolator modifications to the relay control circuitry of the SB200 only require 2V at about 3mA to be switched.? ?Many other amplifiers can probably be switched on and off with only a very few mA as well.? ?? Construction suggestions:? ?see photos. |
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Looks nice!! Gordon KX4Z On Sun, Nov 3, 2024 at 6:48?AM HA3HZ via <gyula=[email protected]> wrote:
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I learned here how to get the cool little handheld device that checks out semiconductors. ?What a fantastic device!!! ?I bought one of those hundred for $8.00 2N7000 assortments from Amazon,…. and only about one out of five is actually a MOSFET!!?
Gordon kx4z? |
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On Mon, Mar 17, 2025 at 05:42 AM, Jon / W2JON wrote:
Gordon I’m assuming you know about the ePTT feature in the 64bit deployment? Jon,
if you read carefully, you'll notice that first there was Gordon's external PTT, then it became the current ePTT. I'm only writing this because no one has had the courage to install one.
Of course, all further improvements are the result of getting smarter in the meantime.
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Gyula HA3HZ |
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Gordon,
your basic idea was used for ePTT, with the difference that you can turn it on/off from the program menu and it has a delayed turn-on (sequencer). Instead of the TX signal, it uses the RPi I/O for control, but the hardware design is YOUR merit!
I use your solution without any problems, thanks for sharing. --
Gyula HA3HZ |
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On Mon, Mar 17, 2025 at 05:02 PM, Gordon Gibby KX4Z wrote:
Now I just need to learn how to compile the new version. Does anyone know the proper way to do that? You can read the description if you don't remember the process. I document every modification step by step, so I can always look back at how I did it.
I see that you solved the installation. Always enter the given directory where you want to do the installation.
If you missed following the development, it is worth loading the sBITX-Toolbox v3.01, because there are many new things in it. In sbitx v4.4, a lower driver level is enough for the same output power. The thing only appeared because I use it with constant voltage and current limit. --
Gyula HA3HZ |
HA3HZ