Optimum supply voltage?

Discussion about this major DATV Project. See https://wiki.batc.org.uk/The_Portsdown_Transmitter
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g3yjr
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Joined: Sat May 23, 2020 1:37 pm

Optimum supply voltage?

Post by g3yjr » Thu Jun 02, 2022 4:24 pm

I'm trying some transmission tests across the bench on 2.4 GHz, using just the Lime Mini output into a small rubber duck antenna and receiving on Minitiouner/Minitioune.

A static testcard decodes fine. The constellation looks good. MT shows no red error bar or error lights.

I've increased the supply voltage to the RasPi4, screen from 5.1V to 5.2V. The power goes to pins 4 and 9 on the GPIO connector. The Lime is supplied from the USB2 socket on the RasPi4.

PD4 Info still says "Low supply voltage now".

The 7" screen shows a little yellow lightning bolt in the top RH corner. Is that a low voltage indication?

What is a safe maximum voltage? I have a 5.6V zener crowbar.

Graham

g0mjw
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Re: Optimum supply voltage?

Post by g0mjw » Thu Jun 02, 2022 9:51 pm

For the PI4, 5.3V - but you shouldn't be seeing the lightning bolt at 5.2V. Are you sure it really is 5.2V? In any case it appears to be working OK. Next test some moving images?

PE1CHY
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Re: Optimum supply voltage?

Post by PE1CHY » Fri Jun 03, 2022 7:09 am

Power supply problems can occur when the internal resistance of the powersupply(inlcuding the wiring to the PI) is too high. This is hard to see with a multimeter. Use a good supply and thick wires. Also an electrolitic capacitor of 1000uF or more soldered directly over tho power input connector of the PI helps.
The capacitor delivers the short current pulses the PI draws.
Rob K
PE1CHY

G8GKQ
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Re: Optimum supply voltage?

Post by G8GKQ » Fri Jun 03, 2022 10:13 am

Hi Graham

For the Raspberry Pi 4, I always feed the supply volyage to the GPIO pins. Then I use thick (RS 16/02) supply leads from a low impedance power supply.

I set the supply voltage to be 5.2v at the pins under load. Finding a well regulated power supply for 5.2v at 2 or so amps then becomes the major challenge.

Brief transients below 4.8v (ish) will trip the low voltage monitor, but should not cause major issues. A continuous lightning bolt shows that the voltage is continuously low and needs attention.

Dave

g3yjr
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Re: Optimum supply voltage?

Post by g3yjr » Fri Jun 03, 2022 2:30 pm

I have thick wire to a bit of connector block where the voltage is measured, then spindly DuPont wires to the GPIO, so there may be a slight voltage drop to the GPIO. I'll move the DVM wires to the GPIO & investigate further.

A capacitor on the RasPi is a good idea.

Thanks to Mike, Rob and Dave for your tips.

73 Graham

g0mjw
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Re: Optimum supply voltage?

Post by g0mjw » Fri Jun 03, 2022 2:42 pm

Dupont wires from Ebay? If so, I am surprised they have not melted. That's your problem.

g3yjr
Posts: 82
Joined: Sat May 23, 2020 1:37 pm

Re: Optimum supply voltage?

Post by g3yjr » Sat Jun 04, 2022 9:06 pm

I swapped out the few cm of flimsy wires & put an even shorter length of fatter wires in, with an extra low-ESR capacitor near the GPIO for good measure.

Neither the RasPi nor the screen complains about high voltage now.

What would make it tidier would be a break-out connector for the GPIO connector. At the moment, I have a collection of 1F and 2Fs pushed onto the pins. I may have a board somewhere. I know I bought some other bits of board from Dave at Finningley a while back.

Thank you for your help.

73 Graham

g0mjw
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Re: Optimum supply voltage?

Post by g0mjw » Sat Jun 04, 2022 9:56 pm

This sort of thing ?
Interface.jpg
Interface.jpg (159.01 KiB) Viewed 3046 times

g3yjr
Posts: 82
Joined: Sat May 23, 2020 1:37 pm

Re: Optimum supply voltage?

Post by g3yjr » Wed Jun 08, 2022 12:07 pm

Very natty with the fan Mike!

I'm sure I have a board somewhere...

73 Graham

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