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tlfong01

Posts: 1312
Joined: 2018-Jun-02 Sat 9:43 pm
Location: Hong Kong

RE: RASPBERRY PI + RELAY GPIO DONT WORK

Postby tlfong01 » 2019-Jan-29 Tue 2:07 pm

PhatFil wrote: 

2019-Jan-29 Tue 10:17 am

the relay … looks like one i have used with a 3.3v arduino, the 5v vcc input is used to switch the relay and an on board transistor uses the 3.3v in signal to switch the 5v vcc feed to power the relay coil, so the relay will use more than 5ma but only 5ma from the gpio is needed to switch the transistor ->the relay. ** I think**

Get around for Arduino Only Relay – Part 1

I agree. Let me use the 5V high level trigger relay module KY019 as an example.

KY019 High Trigger Relay Module Spec
https://www.raspberrypi.org/forums/view … 8#p1323061

KY019 High Trigger Relay Module Schematic
https://www.raspberrypi.org/forums/view … 5#p1325269

1. Rpi GPIO High signal of about 3V at the input terminal of the module drives the PNP BJT SS8050, with a current of about 5mA .

2. SS8050 amplifies the 5mA current to about 50mA and switches on the Songle 5V relay.

3. Songle relay NO terminal is now closed, passing 5/12/24/110/220V DC/AC current of up to 10A to turn on fan, heater etc, …

So far so good, it is only the mirror image twin sister of KY019, Low level trigger, using PNP BJT, that causes all the trouble, and make so many miserable Rpi relay newbies weeping in the dark, … :mrgreen:

To continue next post.

Last edited by tlfong01 on 2019-Jan-29 Tue 8:43 pm, edited 1 time in total.
I am an electronics and smart home hobbyist.

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