pnp relay latchup

Postby tlfong01 » 2019-Jan-29 Tue 9:46 am

Dam_Fr wrote: ↑
2019-Jan-29 Tue 7:54 am
I put PIN “0” or “1”, relay stay ON, …
If I put PIN mode to INPUT mode instead of OUTPUT mode, the relay off, …
Why it’s not working when mode is output on the PIN ?

Relay always On either GPIO outputs Low or High, Off only if GPIO set to input

The For Arduino Only Relay Spec
The low trigger on relay is designed for Arduino whose output Low is similar to Rpi, but its output High is about 4V, much higher than Rpi’s output about 3V.

The Problem
1. Both Arduino Low or Rpi Low can switch the Low trigger On Relay. No Problem.
2a. Now the problem. Arduino’s High of 4V switches off the relay, which is designed to switch off by 4V or above.
2b. But Rpi’s High is only 3V. The Relay doesn’t like it, therefore does nothing.

…..In short, Rpi GPIO High is not high enough to switch off the relay.

Get Around and Risks
1a. To switch off relay, set Rpi GPIO pin to input put mode
1b. Risk 1 – The Arduino guys would LOL the stupidity of Rpi guys,
1c. Risk 2 – Less than 5% chance (my guess only) that Rpi ages faster, or gets fried sooner or later.
2a. / to continue, …

1. Throw away the Arduino only relay, buy a High trigger one instead.
2. Shift up the Rpi 3V3 GPIO signals to 5V0, problem would disappear.

Relay JinJa Question
Why a relay is called a relay?

AliExpress 5V 1 Channel Relay Low Level Tirgger for Arduino
https://fr.aliexpress.com/item/Free-Shi … 6c37UrcD2j

for_arduino_only_2019jan2901.jpg (80.46 KiB) Viewed 1502 times
Last edited by tlfong01 on 2019-Jan-29 Tue 11:23 am, edited 2 times in total.
I am an electronics and smart home hobbyist.


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