Vout in HiZ mode question

General
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I’m using the BP6 as a N-Channel volt meter. That is, I am having problems powering up with a multiple component board - the Wispier

I’ve connected multiple BP leads to the different devices, measuring the voltage on each one. I’m simply using the BP in HiZ mode, so it shows me the different Vcc voltages on the different parts.

My question is - what does the value on Vout show? I haven’t enabled the power supply, but I see various values on Vout.

The board has two ESP32-WROOM boards, and while Vcc and Gnd are tied together, I should be able to power up both CPU’s using either USB connector. However, it only works if I connect two USB cables to the device.

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I need to see the schematic to give you a technical answer, but when VOUT is not powered there is some acceptable leakage through various protection components and diodes. It should generally be 0.6 or 0.7 volts. This is also effected by temperature.

I agree it is a bit freaky. You don’t usually see a measure of floating pins or back powered power supplies, so seeing that it doesn’t sit at ground can be disconcerting. To best of my knowledge everything should be within limits, and many of these will disappear when you touch the pin with a 10M or 1M multimeter probe.

I could be wrong! Bugs are always included for free :slight_smile: I will have a look tomorrow and see what path it might be taking on the 6.

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I don’t have a schematic, but the Wispier is very similar to the Signal Sleuth and the Wardriver. The biggest difference between these is the attached battery pack and the BW16.

I’ve built all three. The last two work fine. But the Wispier, which has two ESP32-dev boards sharing Vcc and GND (according to my DVM).

What should happen is when I power up the board by plugging in the USB cable to Board A, both boards ESP32 boards should power up, as indicated my the power LED.

Instead, when I plug in a cable into board A, only A’s LED lights up.
And when I plug in board B, only B’s LED lights up.
The Wispier board works when I use two USB cables to power A and B.

Yet the power rails are common!!!

I’ve changed software, cables, power sources, etc. The Signal Sleuth in almost identical, and that works fine when I do the same thing.

So I used the BP to measure the VCC on the boards, the GPS and the display, using a cable connected to board A, B and both
Here are the voltages measure on the Vcc pins:

               B          A       Both  powered

Display 1.0 3.2 3.2
GPS 1.0 3.2 3.2
Board B 4.4 0.5 4.4
Board A 4.4 0.5 4.4

I’ve triple-checked for bad solder joints, old software, etc. If anyone has advice on what to check next, I’d really appreciate it.

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One possibility is that vcc could be multiple things. 5v from the usb connector, 3v3 from A regulator. I do not have that kit but the wroom modules are on dev boards and the handling of vusb may be different. Some esp Dev boards will expose the 5v from usb so you could cross power and some do not. I would suggest plugging in two usb cables to the boards and see whether vusb on one connects to vusb on the other ..

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I was thinking along the same lines as lawrence.

In addition:

I’m going to presume those dev boards can be powered from Vcc… verify this first.

It sounds like what you’re doing is using the dev board’s on-board voltage regulator to go from Vusb to Vcc (3V3?). One area I’ve found dev board clones cutting costs is on the voltage regulators.

If you supply power to Vcc directly from an overpowered source (e.g., desktop power supply), do either / both dev boards light up?

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I don’t want to blow up anything so I want to understand.

Are you suggesting I plug board DEV boards into a common power source (hub, laptop with two USB ports).
And I should see if the voltages on pins 3V3 are the same?

I did notice something odd. I have a DVM on GND on board A, and when I measured the voltage of the 5V pin on board B, BOTH power LED’s lit up. In other words, measuring the voltage using the DVM “fixed” the problem. Call me Heisenberg.

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I have a programmable power supply. I can program it for 5V and apply directly to the GND and 5V pins of a board. What sort of amperage should I use?

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No power on two cables just a continuity check between the 5v pin on both usb cables to see whether one cable should power up both . The esp32 modules are 3v3 and I suspect that they depend on separate voltage regulators

This is part of issue, the power setup could cross link the output of the 3v3 regulator on each esp32 dev board but sounds unlikely…

Have you queried with the whisper whether it should run with just one cable or needs both.

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The 5V pins have continuity without any cables.
the 3V3 pins are not connected together (without any cables).

I can look at the serial ports of both boards, and they operate correctly.
Of course, when I just use 1 USB cable, the output indicates only one board is running.

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To follow up, I finally found the problem. My mistake - assuming the pre-soldered headers were done correctly. The 5V pin on one of the boards was bad.

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Argh! That’s so common there should be a simple test for it.

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those errors are the worst. you trust the premade stuff and then it bites you in the ass…

i remember a similar annoying bughunt which boiled down to a 3.5mm audio jack to 2x cinch adapter having left and right mixed up… once beeped out that shit was clear as hell. some heatshrink fixed that error.

Earlier at the same project a diferent audio cable adaptor went bad and trolled us. booked a express ticket to the trash

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I believe @dreg had an early bus pirate 5 that had the same issue on the VOUT power pin. Spi flash chips were having issues because high current operations didn’t have enough juice. Touching the VOUT header pin solved it.