I have connected a relay to BCM 14 and by setting its output to HIGH I can turn it on, making a 220V bulb to turn on.
I use for that the following python instructions:
GPIO.setmode(GPIO.BCM)
GPIO.setup(14, GPIO.OUT)
GPIO.output(14, GPIO.HIGH)
However, if I power off the pi, the bulb remains powered on, and obviously I can’t control it anymore.
After restarting the pi, the gpio readall outputs:
+-----+-----+---------+------+---+---Pi 2---+---+------+---------+-----+-----+
| BCM | wPi | Name | Mode | V | Physical | V | Mode | Name | wPi | BCM |
+-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
| | | 3.3v | | | 1 || 2 | | | 5v | | |
| 2 | 8 | SDA.1 | ALT0 | 1 | 3 || 4 | | | 5v | | |
| 3 | 9 | SCL.1 | ALT0 | 1 | 5 || 6 | | | 0v | | |
| 4 | 7 | GPIO. 7 | IN | 1 | 7 || 8 | 1 | ALT0 | TxD | 15 | 14 | <<<< Bulb Relay
| | | 0v | | | 9 || 10 | 0 | ALT0 | RxD | 16 | 15 |
| 17 | 0 | GPIO. 0 | IN | 0 | 11 || 12 | 0 | IN | GPIO. 1 | 1 | 18 |
| 27 | 2 | GPIO. 2 | IN | 0 | 13 || 14 | | | 0v | | |
| 22 | 3 | GPIO. 3 | IN | 0 | 15 || 16 | 0 | IN | GPIO. 4 | 4 | 23 |
| | | 3.3v | | | 17 || 18 | 0 | IN | GPIO. 5 | 5 | 24 |
| 10 | 12 | MOSI | ALT0 | 0 | 19 || 20 | | | 0v | | |
| 9 | 13 | MISO | ALT0 | 0 | 21 || 22 | 0 | IN | GPIO. 6 | 6 | 25 |
| 11 | 14 | SCLK | ALT0 | 0 | 23 || 24 | 1 | OUT | CE0 | 10 | 8 |
| | | 0v | | | 25 || 26 | 1 | OUT | CE1 | 11 | 7 |
| 0 | 30 | SDA.0 | IN | 1 | 27 || 28 | 1 | IN | SCL.0 | 31 | 1 |
| 5 | 21 | GPIO.21 | IN | 1 | 29 || 30 | | | 0v | | |
| 6 | 22 | GPIO.22 | IN | 1 | 31 || 32 | 0 | IN | GPIO.26 | 26 | 12 |
| 13 | 23 | GPIO.23 | IN | 0 | 33 || 34 | | | 0v | | |
| 19 | 24 | GPIO.24 | IN | 0 | 35 || 36 | 0 | IN | GPIO.27 | 27 | 16 |
| 26 | 25 | GPIO.25 | IN | 0 | 37 || 38 | 0 | IN | GPIO.28 | 28 | 20 |
| | | 0v | | | 39 || 40 | 0 | IN | GPIO.29 | 29 | 21 |
+-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
| BCM | wPi | Name | Mode | V | Physical | V | Mode | Name | wPi | BCM |
+-----+-----+---------+------+---+---Pi 2---+---+------+---------+-----+-----+
So, even after the pi turns back on, the bulb remains turned on anyways until my script runs and when GPIO.setup(14, GPIO.OUT) is executed, the bulb turns off.
I would like to turn off the bulb if the pi goes down (it shuts down/disconnects from the internet – but that is another case I will treat in my script etc).
Should I use other pins for relays? Should I inverse the relay usage (LOW for ON and HIGH for OFF)?
I cannot figure this out and it is a little bit because sometimes the pi disconnects and I have to manually stop the electricity of the bulb.
By using BCM 8 (OUT, 1 by default, after restart), and using LOW output to turn on the relay, the bulb is turned off after restart, but obviously the issue is that as long the pi is completely disconnected from electricity, the relay close the circuit of the bulb.
In short I have the following cases/problems:
BCM USED DEFAULT STATE RELAY ON PROBLEM
14 ALT0 1 HIGH Bulb remains turned on after restart,
until I set the STATE to OUT 0
8 OUT 1 LOW Bulb turns on when pi is disconnected
Expected scenario: always turn off the bulb when the pi disconnects, turn on the bulb only from the script
You do not understand the way GPIO work.
You can control GPIO pins, setting High or Low, and the pins retain their state, even if the Pi is shutdown.
When you remove the Pi power the pins become undefined.
On re-applying power the GPIO pins are configured as INPUTS, with either a weak pullup or pulldown, which depends on the pin.
The pins ONLY become active outputs if configured by the user.
A well designed peripheral will not be activated by the weak pullup or pulldown.
The conventional solution, is to provide a sensible pullup or pulldown (4.7kΩ or less) to force the state, until the pin is configured as an Output.
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What do I need to provide that pullup/pulldown solution? I didn’t know that the pin state is preserved after shutdown. Maybe another solution is to cleanup the pins right before the shutdown. – Ionică Bizău 4 hours ago
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If you want the state to change on shutdown it is your responsibility to implement this. Many circuits implement pull-ups to ensure a safe state. If they do not you can use a resistor, but it is not possible to specify without knowledge of the circuit. – Milliways 4 hours ago
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Can you post an example I should follow to implement this? I do have a resistor I used to turn on an LED. – Ionică Bizău 54 mins ago
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LOWto turn on the bulb, and it works in the sense that after the pi is restarted the bulb turns off, but after turning off the pi, the relay is still in the same position. – Ionică Bizău 5 hours agoOUT 0would help, meaning, that mode is set by default toOUT, but current isLOW. – Ionică Bizău 5 hours agoINandOUT 1are going to turn on the bulb. So, is it possible to configure anOUT 0by default? – Ionică Bizău 1 hour agoOUT. – Ionică Bizău 17 mins ago