I found in one of my drawer some components which are "SIP-1A05 Reed Switch Relay for PAN CHANG"
Not sure where and when I got them from but can see them available on eBay pretty cheap
I get that they are driven by 5V, can support driving 1 amp from the description, I'm wondering if anyone knows - before I start measuring (yes lazy me) - if those include a protection diode or not? a quick look up on line and on vendor sites did not provide the information
(yes, they are probably crappy components, I'm aware of the MAGNECRAFT W107DIP-5 which are probably better and do include the diode but the first ones would fit better in a tight space I have in a hack I'm working on at the moment)
Yes, the first you do with unknown components is get out the meter, it will answer questions with
certainty! You can determine the winding resistance, presence/absence of a diode, and whether its
NO or NC, as well as confirming the pin-out....
(Long story short that drawer i grabbed the things from is in a place where I don't have all my gears - just an arduino à breadboard, some leds and wires)
Good point on the polarity - indeed there is no marking. I'll give it a go at home
Side question given the resistor is about 500 ohms what risk is there for my arduino if it drive the solenoid directly from a pin ? Am I really pushing the envelopper there? (Practically not theoretically) - (draws about 10mA from the pin)
Side question given the resistor is about 500 ohms what risk is there for my arduino if it drive the solenoid directly from a pin ? Am I really pushing the envelopper there? (Practically not theoretically) - (draws about 10mA from the pin)
(I tried with no bad outcome with a couple tries)
Then the real question is: did the reed close at that current?
( well to be honest there is a small noise like the relay closing - did not try further with an heavy load - Will investigate further when I have access to more equipment )
( well to be honest there is a small noise like the relay closing - did not try further with an heavy load - Will investigate further when I have access to more equipment )
Then you are good to connect directly to an Arduino pin and +5 volts on the other side, and connect the protection diode.
The internal pin protection diode between pin and ground will catch the spike, but for how long.
Just connect a small schottky diode across the coil, and move on.
Leo..
Paul - I suppose at 200MHz (or borrow a 500MHz) sampling I could see something
Yes Leo - it was more a theoretical question i was asking myself and the wisdom-hive of contributors here, with such a small coil (and inductive load I will have) how bad can the back EMF voltage spike really be. The next question would be how long will it take for a small diode with a fwd drop of 1V to dissipate the associated power (I've used Metal Oxide Varistor in some cases to make that quicker with large electro-magnets).
A MOV is useless here, since the pin protection diodes clamp the kickback at -0.7volt,
assuming you have connected the coil between pin and ground.
Use a schottky with a lower Vf than the internal pin protection, e.g. the common 1N5819.
Leo..
Yes at this stage the idea is pin -> coil -> ground (considering adding a small R in series as I've read those component might become faulty and the 500 ohms R drops close to 0)
Agree a MOV is overkill anyway for this small element - this is purely intellectual curiosity, thx for the answer
J-M-L:
Agree a MOV is overkill anyway for this small element...
I think you have missed the point.
A MOV is basically a resistor that conducts when a certain voltage threshold is reached.
Kickback voltage, if a relay connected to an Arduino pin, is LESS (0.7volt) than operating voltage (5volt).
Therefore a MOV is useless here.
Just use a schottky diode (Vf <0.5volt) across the coil (cathode to pin).
Leo..
Yes.
A MOV is non-polar device (same clamp voltage in both directions).
It has to be >5volt to not conduct at normal (5volt) operation.
Kickback voltage is lower than normal operation (but negative).
The internal diode will start conducting at ~0.7volt, long before a (e.g. 20volt) MOV would.
An external schottky ! diode (Vf <0.5volt) will conduct before the internal (Vf 0.7volt) diode.
Leo..
did a quick test to see what's happening in real life now that I've access to my scope (200MHz) - nice spikes between 40V and 200V are pretty consistent
(not unexpected)