5V Relay on pycom

[Kebson]

Hi all,
I have a pycom with the LoPy integrated.
I would like to push up a relay, but I don't know if what I'm doing is well.
I have a water pump motor joined to the relay. When I connect the pycom to my machine, I heard the relay sound noise, but nothing else.
I did it like this.

p_relay = Pin('P11', mode=Pin.OUT, pull=Pin.PULL_UP)
while True:
p_relay.PULL_DOWN
print("OFF for 2 seconds")
time.sleep(2)
p_relay.PULL_UP
print("ON for 2 seconds")
time.sleep(2)

Is it a good sample for starting ? Do you have any other idea?

Note that I have a AC/DC adapter, how can I joined it to my relay?

[timh]

@kebson You will need to check the specs of the relay to see what voltage and current is required to actually hold the relay closed.

ESP32 details can be found here
https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf

[robert-hh]

@kebson What kind of relay is that? In any case, you need a switching transistor (like a simple N-Channel Mosfet [e.g. 2N7000]) and a flyback diode [e.g. 1N4148]) to switch the 5V the relay needs. There are some modules which have that integrated, but the circuitry is so bad designed that it still needs a 5V level to fully switch.

[Eric73]

@Kebson
I'm not sure about pycom lexical, but in electronics, pull-up and pull-down is used for input pin only (not push-pull output as you configure your pin). If you want to drive your relay with a low value on your pin use "p_relay.value(0)" and "p_relay.value(1)".
Please note that if you have directly connected your solenoid to the output of your device it's insane and will not work (even you can destroy your pycom device if you haven't a free wheel diode) (output pin of pycom device cannot source more than few milli amp, and can sink about 10mA max). You must use a transistor NPN or fet to drive more current as robert-hh said.

[Kebson]

Thanks for the response,
My relay is like this.

Yeah I heard I must have a transistor, but when I connect it, nothing happens, and if I deconnect if, I heard the relay noise.
@robert-hh @timh @Eric73

[robert-hh]

@kebson The picture in the link shows a transistor and and a flyback diode on the board. And the text tells about 3.3 and 5V compatibility.
The in the code above, to swich the output, you have to issue:
p_relay.value(1)
and
p_relay-value(0)
to switch the output to high and low. You may also write:
p_relay(1) and p_relay(0).

[Kebson]

@robert-hh Ok I will try it in a few minutes to see.

[Kebson]

@robert-hh I try what you said but, nothing special

p_relay = Pin('P11', mode=Pin.OUT)
p_relay.value(1)
p_relay.value(0)
while True:
   if result_dht.is_valid():
        p_relay(1)
   else:
        p_relay(0)

Is there something wrong in the code?

[robert-hh]

@kebson I do not understand why you have that:

p_relay.value(1)
p_relay.value(0)

at the beginning, because that gives just a 3µs pulse at the output. Besides that I assume, that you want to switch the relay on, when result_dht.is_valid() returns True.
If you have a voltmeter, you should see output P11 change it's level. If it does, the program logic is OK, but the relay board does not switch with 3.3 V.

[Kebson]

@robert-hh YEah I commentend the second line, but yes, I would like to put the relay on when result_dht returns True. and turn it off otherwise.
Yesterday, I joined the relay with a transistor, a resistance, but nothing happened. That's why, i disconnect the transistor, and now, it's directly connected on the 3V3 pycom.

[robert-hh]

@kebson Can you post an as-good-as-possible picture of the upper and lower side of the relay board. The upper side should show the transistor and the LED. Then I can derive the schematics.

[Kebson]

@robert-hh

[robert-hh]

@kebson Thanks. Did you ever see the LED turning on. And if yes, what's the color?

[Kebson]

@robert-hh Yeah, when I connect the pycom on the machine, the LED turns on in RED color and I heard a little sound. But he does it once in two.

[robert-hh]

@kebson Is the relay Vcc connected to 5V or 3.3V? And again, what is the color of the LED? Red or green or yellow or blue? It is important, because from the color I can tell the voltage dop of the LED.

[Kebson]

@robert-hh I edited my last answer and put RED color. The relay VCC is connected to my first pin (Vin (3.5-5.5V)).

[robert-hh]

@kebson Red is ok. That has a drop voltage of about 1.4 V, and should work with 3.3 V input voltage. The Vcc input at the board should be 5V, if the device is connected to USB. You could try to bypass the LED and connect the P11 output to the point indicated by the arrow in the picture below.

[Kebson]

@robert-hh It's what i did, but like i said, I just heard a sound, and see the LED turns on, but nothing else.

My relay if it will work, I would like to connect it to a water pump. So, if I can't have the steps on turns on and off the relay, I couldn't continue.

[robert-hh]

@kebson What do you expect from a relay? It is just a solenoid operated switch. When it turns on, you hear a sharp click, it if turns off, you'll hear a soft click. In order to tell if it is working, you have to switch something with it.

[Kebson]

@robert-hh yes, and it's my water pomp I will switch with. But for now, I just would like to see its turns on and off. Because it doesn't. I'm using a transistor P2N2222 to try with it now.