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Low 8 channel shifter voltage reading
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Low 8 channel shifter voltage reading

by donsatchell on Tue Jan 11, 2022 2:56 pm

I purchased four 8 channel voltage shifters (order ID number 2417312-3231552029 ). I connected the VCCA & OE to a 3.2 voltage source (a Teensy 4.1). I connected VCCB to a 5 volt source and have a common ground for all connections. When I alternate the the A1 voltage between 0 and 3.2 volts the B1 voltage alternates between 0 and 2.5 volts, rather than 0 and 5.0 volts. I used a volt meter to verify these readings. When I run the same experiment with 4 channel shifter, I get the expected 5 volt reading on the high voltage side. What could be the problem

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Re: Low 8 channel shifter voltage reading

by mikeysklar on Thu Jan 13, 2022 7:57 pm

Sounds like potential wiring issue. Can you post some photos of how you connected everything and any soldering you might have.

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Re: Low 8 channel shifter voltage reading

by donsatchell on Fri Jan 14, 2022 11:14 am

Attached is a picture of the level shifter test setup. VCCA is connected to a 3.2 volt DC source. VCCB and OE are connected to a 5 volt DC source. Then, the shifter ground is connected to the other grounds. I used a volt meter with the negative probe on the shifter ground solder bead and the positive probe on the VCCA, OE, and VCCB solder beads to confirm the voltages. Next the Teensy 4.1 provided a 3.2 volt signal to A1 that alternated between 3.2 and 0 volts every five seconds. I confirmed the voltage using my voltmeter with the negative probe on the shifter ground solder bead and the positive probe on the A1 solder bead. Then, I measured the B1 voltage using the same method. The voltage alternated between about 2.6 and 2.1 volts. I repeated the experiment with the A1 to A8 channels with similar results. Next, I repeated the experiment with two other 8 channel shifters that I received in the same order with similar results. I did not solder the fourth shifter to keep it available for any additional test that you might suggest. Then I repeated the experiment with a Sparkfun 4 channel and observed alternating voltages between 0 and 5 volts, as expected.
I can see only two explanations for these observations. Either a poor solder connection has resulted in poor communication with the board or the board is malfunctioning. The solder bead look good to me. In addition, I have never encountered problems with my soldering in the past.
Attachments
TestSetup.jpg
TestSetup.jpg (488.93 KiB) Viewed 63 times

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Re: Low 8 channel shifter voltage reading

by mikeysklar on Sat Jan 15, 2022 3:52 pm

Just comparing your wiring with one of our NeoPixel guides that uses the same level shifter I see that we are not wiring in the 0E pin.

Can you repeat your B1 voltage measurement test again without that pin connected?

https://learn.adafruit.com/neopixel-lev ... 2582159-11

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Re: Low 8 channel shifter voltage reading

by donsatchell on Mon Jan 17, 2022 11:09 am

This resolved the problem. Thanks for your help.

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Re: Low 8 channel shifter voltage reading

by mikeysklar on Mon Jan 17, 2022 3:07 pm

That was a wild guess, but glad it worked. Thank you for the feedback.

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Re: Low 8 channel shifter voltage reading

by donsatchell on Mon Jan 17, 2022 5:51 pm

Unfortunately, I declared success to quickly. When I operate the shifter with floating, it works sometimes and not others. The TI manual specifically states that one should no operate the shifter with the OE floating. They state that the OE pin should be connected to the low voltage source, as I originally configured my project. Unfortunately, the Adafruit shifter never worked properly with this configuration. Out of frustration, I purchased a cheap Hiletgo 8 channel shifter and ran is in the original configuration. I worked perfectly first time. As a result, I plan to use this shifter in my project.
Attachments
Hiletgo.jpg
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Please be positive and constructive with your questions and comments.