Pin 3 -

[Ravi Miranda]

Hi everyone,
Having recently wired up the Radioberry to relays, driver boards, T/R
relays and the rest. I seem to have stumbled on a strange behaviour of
Pin 3. I will outline my observations below.

When the Pi is booted up the voltage at Pin3 (Radioberry board) goes
to 3.3 V till the splash screen is displayed, at which point it drops
to 0 volts.

The second instance then occurs when the pi is shutdown. At this
point, the voltage goes high to 3.3V and stays then after the pi is
fully shutdown.

I ask this since I'm using the pin to drive a ULN2803 and then has a
cascade effect of driving the T/R relay to on and the bias to the PA
etc.

Has anyone seen this issue before? Any thoughts on how this could be
resolved/has been resolved would be appreciated.

Best 73

Ravi/M0RVI

--
I'm here to add more value to the world than I'm using up.

[Ricardo Suarez]

Yes, my radioberry does the same thing, locking TX signal to the output
module (scrapped from an Yaesu FT-747) on tx state at boot and at shutdown.

Rick LU9DA

[Mario Vano]

Funny you should mention this!

 I'm finalizing the design of my LPF/VSWR/Relay board that stacks with the radioberry here and have encountered the same problem on my 3 prototype boards. They basically use band switch commands compatible with the N2ADR filter board so no software needs to be reconfigured.

I'm not an expert on gate arrays, but it appears to me from the data sheet that the Intel gate array output pins are guaranteed to come up from a power down state neither HIGH nor LOW - but somewhere in between. There's a confusing table of best and worst case values in that document.

I have estimated a worst case for the situation to be fixed using a 3.9k resistor from pin 5 to ground. This seems to be enough to keep below the ULN200x series darlington threshold at power up on my 3 prototype systems. After initialization, the pin goes to a more solid 3.3 V. and the 3.9k resistor does not appear to be loading the signal in any way.

Note that the N2ADR board in the HL2 uses a few more  gate inversions to act on the TX signal and disable the HPF in hardware from the gate array and the subsequent gates all happen to come up correctly in that radio without needing any fix. As we are all discovering, driving a darlington relay driver directly from the pin is a bit different situation - especially because loading the board from software may not always occur in cases where the software driver is missing or disabled in some other way.

The only nuisance is that if you apply the resistor to the radioberry board, the ground is at the other end of the connector, so you have to use a TH resistor with longer leads.  I've put the resistor into the next rev for my PCB, but for now, the prototypes all have the resistor hanging under the radioberry's connector to fix the problem.

By the way, if anyone has any problem using the 3.9k value for a fix, please let me know so I can adjust the value here...

Hope this helps...

Mario - AE0GL

[Mario Vano]

Correction: I meant the tx becomes solidly either 0 (when idle) or 3.3V when active after the pins are initialized.

[Ravi Miranda]

Thanks Mario, for the excellent analysis, I think I might ditch the
use of Pin 3 to drive the relay/s but rely instead on an external
optocoupler to switch relays directly from the PTT. Will try this
shortly.

Kind regards,

Ravi/M0RVI

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[Mario Vano]

I was initially using a different method to trigger my antenna relay and power amplifier and that worked fine, but I decided that it would be better not to add another non-standard step in the T/R timing, since the FPGA and most app programs already do some sequencing that assumes no one else is doing it. That's why I went back to pin 3....

Good luck to all with their projects!

M

[Ravi Miranda]

All,

Apologies for bringing this up again. I put the project on the back
burner to sort out a few other things.

I was wondering if there are any new ideas that others have tried
successfully to ensure that the TX does not go high on start or
shutdown?

Thank you for your time.

Best 73,

Ravi/G1RVI (formerly M0RVI)

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[Mario Vano]

Ravi, I've had no trouble with this problem since installing 3.9k resistors from that pin to ground. In fact, they ended up incorporated in my LPF board design so I no longer have to have them hanging on the Radioberry any more. Before that, I was soldering them on to the board on the opposite side from the connecter.

By the way there is nothing dodgy about this fix at all. Consulting the data sheet for the gate array, I discovered that the part's power up behavior was exactly as described by Intel, so the need for the fix is quite legit.

The only other news I have about this pin is that I discovered that the very common ULN2003 I was using in all my designs connected to  to the pin works fine when it's the ONLY part being driven by the gate array, but that it has no current limiting resistor built in to its inputs. This means it drags the Gate array pin down to about 1.5 Volts when it's active High. This was never a problem until I started trying to connect more than one board to the pin. In particular, boards like the preamp board also use that pin to trigger board behavior. The fix was very simple - in my case, I replaced it with  ULN 2004, which has been designed to eliminate this problem by incorporating series resistors..

I just checked the data sheet for the part you are using and found that it is one of the parts that incorporates the series 2.2k resistors internally, so I don't think that should be causing you any trouble - but I'd still advise people to check the data sheets of the parts they are driving with pin 3.

Hope this helps. I've been operating several complete Radioberry 5W radios I built for quite a while now including for POTA and other park activity...

M