Level shifter DOA?

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vkvarma
 
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Level shifter DOA?

Post by vkvarma »

Hi,

I recently purchased a TXB0104 level shifter, as I was struggling to get a signal from a 5V source to my rpi 4. After connecting and seeing a noisy signal on the pi, I disconnected it from the GPIO pin and poked at it with my multimeter. 3.30V at the LV voltage pin, 5.18V at the HV voltage pin, 5.17V at the signal input, and a noisy ~1.8V (1.55-2.05V) at the LV signal output. Nothing else connected, and I've tried resoldering to each of the signal pin pairs. Same result. 0V on the input produces 0V at the output, so I get a clean low signal, but when the input signal is high, the output is just barely at the threshold for the logical true on the rpi GPIO. double and triple checked the voltage on the LV voltage pin, 3.30 with no measurable noise. What gives?? LV side voltage is way too low. Is there something wrong with the rpi input pin that could have damaged the TXB0104? Shorting the input pin to GND or 3.3V produces a clean low or high.

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dastels
 
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Re: Level shifter DOA?

Post by dastels »

You don't mention the grounds. Are they ALL connected together?

Dave

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Re: Level shifter DOA?

Post by vkvarma »

yup. everything is measured from a wire coming off the rpi ground. ground to the board is technically coming from the 5V side, which is grounded through a bldc esc, but I get a buzz on my multimeter when I set it to the signal test function and test the 5V-side ground and the rpi ground. I've also tested with an external 5V source (provided by an arduino), for which I have the 5V ground forking off of the rpi (3.3V) ground.

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Re: Level shifter DOA?

Post by dastels »

Can you post a clear photo showing the connections to the level shifter board?

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Re: Level shifter DOA?

Post by vkvarma »

Not really; I'll see if I can find a utility to downscale the resolution on my image, but my phone camera far exceeds the 1MB limit. I wired another ground off of the level shifter and plugged it into the arduino providing the 5V source for testing, in case there was some capacitive coupling on the ESC I wasn't able to pick up on with my multimeter. This time, I measured 5V at the input signal, and 2.7 at the output, which got me excited, but plugging into the rpi still gave me a nonsense signal. Disconnecting it and measuring again, I am once again stuck with ~1.6V... LV and HV power pins are still reading 3.3V and 5.18V, measured directly from the ground pin on the level shifter.

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Re: Level shifter DOA?

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update: I bought a second one of the same level shifter in the same order, for a different project. Didn't want to break it out for this, but figured I had to... This one's giving me messed up results in an entirely different way! The moment I plug the 5V signal pin into the level shifter board, it (the signal voltage, not either source voltage) drops to 2.5V. Held my multimeter between ground and the sensor signal wire, and had my partner plug it into the A side, and the moment it made contact, it pulled the input signal from 5.16V to 2.45V. Everything on this board is connected to the same places it was with the other one I tested.

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Re: Level shifter DOA?

Post by dastels »

In lieu of a photo, how are the wires connected to the level shifter board?

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Re: Level shifter DOA?

Post by adafruit_support_bill »

If you search the web for "image resize" you will find plenty of free on-line resizing tools. About 800x600 usually works best for the forums.

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Re: Level shifter DOA?

Post by vkvarma »

levelshifter.png
levelshifter.png (97.37 KiB) Viewed 152 times
I think the diagram does a better job of showing the whole system than an image would, anyway. The RPi is in an enclosure, which is itself mounted in a cabinet I put together for it (which is why I'm testing with an arduino for the 5V source, as the pi is fairly inaccessible), and it'd be difficult to highlight the specific wires coming from the cabinet for this sensor in a photo.

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Re: Level shifter DOA?

Post by vkvarma »

dastels wrote:In lieu of a photo, how are the wires connected to the level shifter board?

Dave
I may have misunderstood this initially. On the first board, they were soldered directly to the holes. For the second, I soldered on the male headers that came with the board, and used jumper wires to connect to the header.

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Re: Level shifter DOA?

Post by adafruit_support_bill »

everything is measured from a wire coming off the rpi ground. ground to the board is technically coming from the 5V side, which is grounded through a bldc esc,
You diagram doesn't show the BLDC/ESC or any of your power sources. But ground is the signal reference for the level shifter and routing it via an ESC is likely introduce a significant amount of noise. I would suggest a direct GND connection from the Pi to the level shifter.

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Re: Level shifter DOA?

Post by vkvarma »

adafruit_support_bill wrote:
everything is measured from a wire coming off the rpi ground. ground to the board is technically coming from the 5V side, which is grounded through a bldc esc,
You diagram doesn't show the BLDC/ESC or any of your power sources. But ground is the signal reference for the level shifter and routing it via an ESC is likely introduce a significant amount of noise. I would suggest a direct GND connection from the Pi to the level shifter.
Yep, the initial setup had ground to the level shifter from the pi, via an esc, through the hall sensor, and then to the level shifter. I was worried about that noise, and so I rewired it as in the diagram. This is how I'm testing now. The ESC is still connected, but only to the 5V and GND from the arduino, and to the signal wires from the hall sensor board. The motor power and control signal wires are disconnected from the ESC.

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Re: Level shifter DOA?

Post by vkvarma »

I can try hooking it up to my oscilloscope tomorrow to get a better picture of what kind of noise is on that ground line, if you guys think that would be helpful, but I'm a little concerned about the two of the exact same board I purchased failing in two distinct ways upon first being connected. It is possible that my wiring is lacking, but I'd expect the same mode of failure in both cases, rather than one not pulling the LV side signal to the LV source level, and the other dragging the HV side signal down upon being connected (with the LV signal totally detached).

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Re: Level shifter DOA?

Post by vkvarma »

bought some similar level shifters off amazon, which I normally don't like to do. They just work, same connection points and everything. I think this might be closer to adafruit's i2c-compatible variant, which I don't need here per se, but they were the first to come up in my search. Either I royally messed up soldering the ones from adafruit (also had to solder the ones from amazon, and multimeter shows no shorts between any pairs of pins, and visual inspection shows no stray solder on any of the pcbs), or they both came DOA.

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