G8TA Portsdown since CQ-TV 278
Posted: Mon Feb 13, 2023 8:41 pm
Hello everyone
I wrote about our club's [Wolverhampton ARS G8TA) Centenary DATV unit for CQ-TV 278. Since the article has been published, 2 developments have occured which are in time to make an entry in the RSGB Construction Competition.
Firstly I found that with CAD and graphics software, no route to a CNC miller nor engraver and a local print shop nearby, I could design a self-adhesive vinyl label. Oxley Stationers and Printers have a full colour plotter capable of A2 widths at least that prints advertising and other glossy labels. The labels are cut to size by the plotter so the paper size has to match the outline of the panel fascia. An A2 print cost £15. Mine featured the words, potentiometer scales and some blue outlines. The unit is electronically colourful already. My wife and I had a challenge to get the label onto the panel. The shop said to apply a mist of water with an atomiser spray. This gives you a chance to have a second go. A dense sponge block is used to wipe the label on to the surface while your partner peels off the backing and holds the leading edge aloft. We came to grief where the aperture for the screen is. No metal here to which to adhere so the label lost its tension and went out of alignment. A second go with the waste piece from cutting out that aperture in place worked. We were relieved and the panel looked superb. An hour with a sharp craft knife to cut out all the holes and openings plus sealing the edges with Scotch magic tape and it was ready to put on.
The second development is the completion of the Rx/Tx changeover controller. I made one of these a few years ago when I started using a 12V non-latching 4 into 1 coax switch and logic gates. It's been great so I wanted to include a similar set up in the club unit. I'd bought a 6 into 1 latching 24V Dynatech switch for £20 in 2019. It'll come in handy if it's ever used.... I made a mounting bracket for it so it sits well on the back face of the unit.
Ron M0RNW has designed a circuit using H bridge control IC’s [SN751410NE which are usually associated with stepper motor control] and written the Arduino sketch for the Arduino Nano V3 microcontroller. This takes the outputs from the 4 band decode board, routes through to the correct PA port and controls Rx to Tx changeover when the PTT is pressed on the touch screen. It sends a latching pulse to the 6 in 1 coax switch to connect the correct port to the centre antenna connection. A small boost converter is on the PCB to make the 24V with lots of filtering too. Sequencing and time delays are done in software. The sketch controls the connection of the antenna to the receiver as a default action. A receive pre-amp can be switched in and out of circuit in sync with the receiver. Band selection and symbol rate are the main parameters controlled from the touchscreen. The software sets up the transmission chain for each band and via the band decode card the selection of external amplifiers and the PTT action.
The PCB arrived from JLCPCB a week ago. I'd built the board that evening. Next evening was a wiring session. I'd left the band decode output and PTT socket wires coiled up ready to go. By 10.30pm all but the indicator lamps and the pre-amp power was wired up. Stripmaster wire stripping and The Engineer Molex KK crimping tools are a wonderful help!
At club on the Wednesday, Ron uploaded the sketch to the Nano. The unit went click and the receive connected LED came on but nowt happened on pressing PTT. Ron hastily altered the sketch and uploaded while the unit was powered. A Nano smells horrible when it releases its magic smoke!
Version 3 of the sketch was uploaded here on Friday and it worked like a charm. The antenna is connected to port 1 receiver. Port 6 is a spare. 2 to 5 are the unit's four bands in frequency ascending order. I made up an LED indicator light set for the big switch's indication terminals. It's proper reassuring to see the correct one lit as the system goes to transmit and the routing to the PA is made. A surprise, nice touch is that the changeover LED flashes twice while it's in the delay portion of the sequence. The video of this working with a mini-kits PA is here https://youtube.com/shorts/x2TjvcakwyY?feature=share.
Ron thinks that a header pin across two of the spare GPIO pins on the Nano could make a neat way to tell the Nano if a latching or non-latching switch is in use. He's troubled by how large the PCB is [but it has to fit in between the card rails] . But for now we have the competition deadline and need some well lit, sharp photos to sell the project to the judges. Afterwards I'll put Gerbers and Schematic on the BATC wiki. The sketch is on Ron's Github page which we'll announce in due course. Hopefully members who have such a coax switch will find this controller a real bonus. It looks a lot simpler than the comprehensive MacGuffin project to me.
73
David M0YDH
I wrote about our club's [Wolverhampton ARS G8TA) Centenary DATV unit for CQ-TV 278. Since the article has been published, 2 developments have occured which are in time to make an entry in the RSGB Construction Competition.
Firstly I found that with CAD and graphics software, no route to a CNC miller nor engraver and a local print shop nearby, I could design a self-adhesive vinyl label. Oxley Stationers and Printers have a full colour plotter capable of A2 widths at least that prints advertising and other glossy labels. The labels are cut to size by the plotter so the paper size has to match the outline of the panel fascia. An A2 print cost £15. Mine featured the words, potentiometer scales and some blue outlines. The unit is electronically colourful already. My wife and I had a challenge to get the label onto the panel. The shop said to apply a mist of water with an atomiser spray. This gives you a chance to have a second go. A dense sponge block is used to wipe the label on to the surface while your partner peels off the backing and holds the leading edge aloft. We came to grief where the aperture for the screen is. No metal here to which to adhere so the label lost its tension and went out of alignment. A second go with the waste piece from cutting out that aperture in place worked. We were relieved and the panel looked superb. An hour with a sharp craft knife to cut out all the holes and openings plus sealing the edges with Scotch magic tape and it was ready to put on.
The second development is the completion of the Rx/Tx changeover controller. I made one of these a few years ago when I started using a 12V non-latching 4 into 1 coax switch and logic gates. It's been great so I wanted to include a similar set up in the club unit. I'd bought a 6 into 1 latching 24V Dynatech switch for £20 in 2019. It'll come in handy if it's ever used.... I made a mounting bracket for it so it sits well on the back face of the unit.
Ron M0RNW has designed a circuit using H bridge control IC’s [SN751410NE which are usually associated with stepper motor control] and written the Arduino sketch for the Arduino Nano V3 microcontroller. This takes the outputs from the 4 band decode board, routes through to the correct PA port and controls Rx to Tx changeover when the PTT is pressed on the touch screen. It sends a latching pulse to the 6 in 1 coax switch to connect the correct port to the centre antenna connection. A small boost converter is on the PCB to make the 24V with lots of filtering too. Sequencing and time delays are done in software. The sketch controls the connection of the antenna to the receiver as a default action. A receive pre-amp can be switched in and out of circuit in sync with the receiver. Band selection and symbol rate are the main parameters controlled from the touchscreen. The software sets up the transmission chain for each band and via the band decode card the selection of external amplifiers and the PTT action.
The PCB arrived from JLCPCB a week ago. I'd built the board that evening. Next evening was a wiring session. I'd left the band decode output and PTT socket wires coiled up ready to go. By 10.30pm all but the indicator lamps and the pre-amp power was wired up. Stripmaster wire stripping and The Engineer Molex KK crimping tools are a wonderful help!
At club on the Wednesday, Ron uploaded the sketch to the Nano. The unit went click and the receive connected LED came on but nowt happened on pressing PTT. Ron hastily altered the sketch and uploaded while the unit was powered. A Nano smells horrible when it releases its magic smoke!
Version 3 of the sketch was uploaded here on Friday and it worked like a charm. The antenna is connected to port 1 receiver. Port 6 is a spare. 2 to 5 are the unit's four bands in frequency ascending order. I made up an LED indicator light set for the big switch's indication terminals. It's proper reassuring to see the correct one lit as the system goes to transmit and the routing to the PA is made. A surprise, nice touch is that the changeover LED flashes twice while it's in the delay portion of the sequence. The video of this working with a mini-kits PA is here https://youtube.com/shorts/x2TjvcakwyY?feature=share.
Ron thinks that a header pin across two of the spare GPIO pins on the Nano could make a neat way to tell the Nano if a latching or non-latching switch is in use. He's troubled by how large the PCB is [but it has to fit in between the card rails] . But for now we have the competition deadline and need some well lit, sharp photos to sell the project to the judges. Afterwards I'll put Gerbers and Schematic on the BATC wiki. The sketch is on Ron's Github page which we'll announce in due course. Hopefully members who have such a coax switch will find this controller a real bonus. It looks a lot simpler than the comprehensive MacGuffin project to me.
73
David M0YDH
