I have a TPIC6C595 controlling a SILK05-1A72-71D relay in my project (or a few of). The operation of the relay is as expected, it turns on when I want it to.
However, with the relay on, there is a lot of 'noise' or something I don't understand on the switch contacts of the relay. Is this just the voltage 'floating' on the switch contacts because they are not connected to anything yet? Or is this the relay inducing a voltage onto the switch contacts?
I am writing to the shift registers in the loop with a simple 'writeRegisters' function, could it be the Arduino loop switching the relay on and off ever so quickly?
void writeRegisters(){
digitalWrite(RCLK_Pin, LOW);
for(int i = numOfRegisterPins - 1; i >= 0; i--){
digitalWrite(SRCLK_Pin, LOW);
int val = registers[i];
digitalWrite(SER_Pin, val);
digitalWrite(SRCLK_Pin, HIGH);
}
digitalWrite(RCLK_Pin, HIGH);
}
It is difficult to know without your entire sketch. Those relays are mechanical devices and they will have noise when contact is first made. The datasheet also says the operation time (including bounce) is 0.7 ms (max). Are you trying to switch them faster than that?
No. I am only toggling on and off the relay when a button is pressed. So this waveform is seen until the button is pressed to move onto the next relay. Then if I move the scope probe to the next relay, you see the same thing.
This is why I am confused. I am not swicthing them on and off or fast. They are on or off.
If I substitute the reed relay with a hf3fa/005-htf the noise is non-existant. Could this just be a dis-advantage to using reed relays?
Or am I missing an electircal principle I should be applying to mitigate against the 'noise' when using reed relays?
With the reed relay I can measure (DMM) 1.2Vdc on the isolated switching contacts whereas I can read nothing from the HF3FA 0.001Vdc. Plus the scope picture of the HF3FA is just background noise, no horrible picture like seen above.
So I currently have 6 reed relays next to eachother, not all on, only 2 max. Just did some reading and...
"Reed relay screening:
One of the issues that can occur with reed relays is that there is magnetic coupling from the coil. Each reed relay assembly will have an associated magnetic field that extends beyond the mechanical confines of the relay itself.
Magnetic field associated with a reed relay
The magnetic field associated with a reed relay
If the magnetic field is not contained, then the field from an adjacent relay or relays can oppose the field within the relay in question. The arrows on the field that pass through the centre of the coil are in the different direction to the external ones. As the internal field from the coil will be affected by the external field from an adjacent relay, these can be understood to oppose one another.
The field cancellation effect reduces the sensitivity, requiring a higher voltage to ensure reliable switching. With close packed relays, an increase of 30 to 40% of the coil voltage would not be an unreasonable figure, and this may exceed the ratings for the relay and also result in excessive heat dissipation."
I am writing to the shift registers in the loop with a simple 'writeRegisters' function, could it be the Arduino loop switching the relay on and off ever so quickly?
Yes, it could be. You may have bunged up something in your sketch. Another idea, the power supply may not be powerful enough to supply the relay current, and is oscillating.
Noise problems usually requires full images, schematics, basically everything you can think of posting that would help people see what you are doing.
Hi,
Do you mean SILK05-1A72-71D or SIL05-1A72-71D ?
They are fitted with back-emf diodes internally so you need to connect to the coil with the correct polarity.
Where did you connect the scope probe and ground when you took those measurements?
If they are floating its probably noise from some part of your project and I wouldn't worry about it.
The HF3FA is a different construction for a start, note it does not have an internal back EMF diode, you will have to fit one.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Can you please post a picture of your project please so we can see your layout?
It looks like you are scoping an unconnected conductor, the open relay contacts. When it's energized, it's connected to "N/C" but I don't know if that is "no connection" or "normally closed" because you didn't show the rest of the circuit. Scoping an open circuit is like scoping an antenna for noise.
