Hi all -
I have a 70 watt latching, pulse controlled solenoid that I'm trying to control with an Arduino.
To do so I'm using a DPDT relay wired in an H bridge configuration (in reality you'll see in the code that I've used two SPSTs programmed to always maintain opposite states...I didn't have a DPDT that could handle 70 watts DC so I went this route for the moment). Supply is a pretty standard 12V 100watt power supply (powering a 5V arduino pro mini via the RAW input). To apply the pulse and ensure that current only reaches the solenoid during the pulse period, a second SPST relay is wired in series ahead of the DPDT on the positive side, so the unpowered SPSTs switch to switch polarity, and the third SPST switches on and off to apply the pulse (relay has a 10ms max operate time, and ON pulse is 100ms, OFF pulse is 900ms with opposite polarity so speed shouldn't be an issue). I made a quick diagram on tinkercad of what the basic circuit looks like (I didn't include the protection diodes across the relay coils, but they are there in the real circuit).
The final design will respond to the rise and fall on a digital signal from a DAQ, but for now Im testing with barebones code that should latch and unlatch every 5 seconds. The solenoid mostly behaves but sometimes fails to latch or unlatch. I've also noticed that while watching the built-in LED that should be ON while latched and OFF while unlatched, the unlatched phase starts to get shorter and ends with a bump of the solenoid and a blink on the LED...this shouldnt be happening as far as I can tell from the code, and also doesnt begin to happen until a few cycles in, so I'm thinking the solenoid may be giving me a big kickback and throwing things out of whack somehow since the Arduino is powered from the same supply...if that's the case I'm having trouble imagining where the protection diode (assuming that's still the solution) would go given the switching polarity. Im also suspicious Im missing something fundamental about how these pulsed latching things work, because early in experimenting I was able to get the thing to latch and unlatch (unreliably) using only pulses and never switching polarity. Is there some way to determine if the polarity relative to the solenoid terminals should be a particular direction for the ON vs OFF, or does it only matter they they are opposite? Switching the leads it's always more reliable in one direction than the other while the program is running, but maybe that's more to do with pulse length?
In the final code Ill get rid of delay and do something more elegant, but for proof of concept that I could provide suitable pulses to operate the solenoid delay seemed fine for such a simple program...but maybe it's also causing some problem I didnt anticipate?
Thanks in advance for any input!
#define relay1 5
#define relay2 6
#define pulseRelay 10
#define button 2
boolean latched = false;
int value;
void setup() {
// put your setup code here, to run once:
pinMode(relay1, OUTPUT);
pinMode(relay2, OUTPUT);
pinMode(pulseRelay, OUTPUT);
pinMode(button, INPUT_PULLUP);
digitalWrite(pulseRelay, LOW);
delay(30);
digitalWrite(relay1, HIGH); //Again - the real circuit uses 2 SPST programmed to recieve opposite signals
delay(30); // to reverse polarity. These two only see power when the "pulseRelay" is HIGH
digitalWrite(relay2, LOW);
delay(30);
debouncer.attach(button);
debouncer.interval(5); // interval in ms
Serial.begin(9600);
}
void loop() {
shutterToggle(latched);
delay(5000);
latched = !latched;
Serial.println(latched);
}
void shutterToggle(boolean state){
if ( !state ){ //latched - i.e. shutter open
digitalWrite(LED_BUILTIN, HIGH);
digitalWrite(relay1, HIGH);
delay(20);
digitalWrite(relay2, LOW);
delay(20);
digitalWrite(pulseRelay, HIGH);
delay(110);
digitalWrite(pulseRelay, LOW);
}else if ( state ){ // not latched / shutter closed
digitalWrite(LED_BUILTIN, LOW);
digitalWrite(relay1, LOW);
delay(20);
digitalWrite(relay2, HIGH);
delay(20);
digitalWrite(pulseRelay, HIGH);
delay(900);
digitalWrite(pulseRelay, LOW);
}
}
