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
Expected scenario: always turn off the bulb when the pi disconnects, turn on the bulb only from the script
NOTE: Please know this answer disregards all comments made to the OP’s question.
The issue you’re facing cannot be solved with software alone. You will need to add some hardware if you wish to maintain positive control of your relay at all times. As made clear in @Milliway’s answer, GPIO states are indeterminate when power is removed from the RPi – that is to say when power is removed from the RPi, the state (HIGH/LOW/OFF) of the GPIO pins is unknown/undefined. It follows then that you cannot maintain positive control of your relay if you allow GPIO pins with undefined states to control it. Once you understand that, you are on your way to a workable solution.
Based on your “Expected scenario”, there is a fairly simple hardware solution outlined in the schematic below. Simply described:
- When the RPi is not powered up, this hardware will force the relay in the schematic to be in its Normally Open state.
- When the RPi is powered up, the GPIO pin will take over control of the relay’s state.
In hardware-logic-speak this is known simply as a AND gate – its “logic equation” in this example is as follows:
IF (RPi IS POWERED) AND (GPIO IS HIGH) THEN (RELAY IS ENERGIZED)
Or, re-phrased to mimic a software idiom:
IF (RPi IS POWERED) AND (GPIO IS HIGH) THEN (RELAY IS ENERGIZED)
ELSE (RELAY IS NOT ENERGIZED)
Notes re Schematic:
- Due to the absence of any hardware specifications in the original question, the schematic shown here omits certain details required for implementation. If you need implementation details, please edit your question to include specifications for your relay (or a link to its spec sheet).
R1&C1work to perform a power-on-initialization of one of the inputs to theANDgate. When power is applied to the RPi, the voltage acrossC1will increase from 0 (GND potential) to 3.3V at a rate determined by the R-C time constant (tc =R1*C1), eventually reaching the supply voltage (3.3V in this case).Consequently, choosing the values of
R1andC1allow you to determine how long the output of theANDgate is forced low – and thereby inhibiting the GPIO output from controlling the realy.- Also know that for situations requiring a very long initialization time, there are alternative methods and designs to accomplish this. Likewise, other features such as fail-safes, hardware interlocks, etc. may be accommodated.
- The warning we give to everyone who dabbles in circuits containing potentially lethal voltages applies for this project. A careless moment can change your life – so develop personal habits and safeguards, and please be careful.
simulate this circuit – Schematic created using CircuitLab
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 21 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 20 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 17 hours ago
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@IonicăBizău without details of the circuitry you are using it would be irresponsible to make circuit recommendations, – Milliways 6 hours ago
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@IonicăBizău: I mostly agree with everything Milliways has said. However, I’ve made some assumptions, and have some ideas for you here. – Seamus 6 hours 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 22 hours agoOUT 0would help, meaning, that mode is set by default toOUT, but current isLOW. – Ionică Bizău 22 hours agoINandOUT 1are going to turn on the bulb. So, is it possible to configure anOUT 0by default? – Ionică Bizău 17 hours agoOUT. – Ionică Bizău 16 hours ago