Make initial pin value configurable.

[soundanalogous]

When an Arduino board boots up, all digital pins default to INPUT. Then when Firmata is initialized, all pins are set to OUTPUT (to avoid transient voltages triggering unmanaged input pins). When the pins are set to output, the value is also set to LOW. It turns out that this can be an issue if someone is using relays.

It may be helpful to suppress setting the output value to LOW on startup or to provide a way for users to specify the initial output pin states (could be worth reexamining the older proposals for saving state in EEPROM).

[cmyang001]

I have the relay problem. Current solution is to set the relay pin to HIGH in systemResetCallback().

[drj-io]

Thanks @soundanalogous - I'll keep an eye on this issue and might look into it further when I have some time.

[Beadsworth]

I had trouble with relays and initial pin states... I am posting my problem and solution here so others may find it more easily.

I have a tiny relay board connected to my StandardFirmata-enabled arduino. If you do not alter the StandardFirmata code, all relays will go CLOSED initially on startup (output pins default to LOW -> CLOSED).

Many relay boards have opto-isolation circuits. You can tell if you see a RY-VCC pin in addition to the normal VCC pin (RY-VCC may be named something slightly different). RY-VCC powers the coils in the relays, VCC controls the opto-circuit. Sometimes you will have to remove an electrical clip that connects the two pins.

The VCC pin, which powers all the opto-switches, draws very little power. You can power the opto-circuit with an output pin (the relay coils, however, require 5V pin). So by attaching VCC to an output pin (and RY-VCC to 5V, making sure VCC and RY-VCC aren't connected -- and of course GND to GND) you can enable/disable the entire relay board with only one output pin.

On boot-up, all output pins default to LOW. So all relays will initially try to be in the "CLOSED" state (relay control pin LOW), but the entire board will be disabled (VCC LOW). This allows you to default relays to OPEN on boot without editing the arduino code. You may then edit the relay control pins at your leisure with pyFirmata, and enable the entire relay board with VCC -> HIGH.

Not really a software solution, but an easy fix if you have an opto-circuit already integrated into the board. For more info follow link:

https://arduino-info.wikispaces.com/RelayIsolation

[troywweber7]

I take @Beadsworth at his word that the Vcc pin draws very little power, but wanted to add my two cents that it probably doesn't hurt to power the Vcc pin through a transistor to add that extra level of security for your Arduino pin.

Otherwise, this solution also worked for me. It still might be nice to have the ability to set the initial state of the pins in your Arduino file, however. This would end up saving you a pin that is otherwise used to control the relay power.

[soundanalogous]

I'm going to eventually change the default pin state in Firmata to digital INPUT rather than OUTPUT, but this requires a few breaking changes so it's not coming until Firmata 3.0 (which has not defined timeline yet).

[bgibbo]

cmyang001 -

I have the relay problem. Current solution is to set the relay pin to HIGH in systemResetCallback().

In the above comment where do you set the relay pin to high in systemResetCallBack.
Im using homeassistant and Arduino with Firmata standard and its causing me pain the fact the outputs are going active low on startup as my relay requires a low to be activated. I have 64 of them. So it would be a pain to build a nand gate hardware solution to solve a software tweak. Any assistance would be greatly appreciated . Many Thanks

[soundanalogous]

Make sure you have the latest version of StandardFirmata. The pin value is no longer set to LOW when the pinMode is set to OUTPUT, unless that pin was previously configured as a PWM pin (which is a rare case): https://github.com/firmata/arduino/blob/master/examples/StandardFirmata/StandardFirmata.ino#L321-L324.

[soundanalogous]

However if you still have an issue, it may be the case that when pinMode is set to OUTPUT that the default state is LOW. If that is potentially the case then add digitalWrite(PIN_TO_DIGITAL(pin), HIGH); after this line.

[bgibbo]

Many thanks for your HeIp, followed your advice and uploaded changes to the firmata. All working. I used this link https://home-assistant.io/components/switch.arduino/ "negate: true" to set ouputs to active High for off and active Low for on. Excellent

[privatesam]

@bgibbo and others. Thanks for this thread. I too am struggling with my Arduino Leonardo board and restarting the application Home Assistant and it firing my doorbell. https://community.home-assistant.io/t/arduino-gpio-activating-every-time-ha-is-restarted-can-this-be-stopped/77459

I intend to make the change suggested in this thread and upload the modified Firmata to my board to deal with this issue. But @bgibbo I just wondered if you were able to clarify the "negate:true" and "initial:true" options in the Home Assistant component in relation to this issue. https://www.home-assistant.io/components/switch.arduino/