Newbie Discussion Notes on 5V/12V High Level Trigger Relay's Input Voltage Requirements V1.0
Brandon92 wrote: ↑
Tue Aug 21, 2018 8:44 pm
- 1. Yes, i would not use the "low setting" ;P
- 2. Yes/No, If the current through the LED, from the optcouple, is big enough so that the tranistor will be fully turn "open"
- 3. Same as above, only then the current is to low
- 4. Okay (as long as the current is save for the arduino)
- 5. Okay (as long as the current is save for the pi)
- 6. This could result in a current that's is to high for the LED inside the optocoupler (not calculated).
- 7. This could result in a current that's is to high for the LED inside the optocoupler (not calculated).
- 8. If the relay is not reated for that kind of voltage. The coil could burn out or the led.
- 9. If the relay is not reated for that kind of voltage. The coil could burn out or the led.
- 10. As long as you are in the "save" operation area of the product, yes
- 11.Same as above
1. Thank you for your comments. I made 15 comments, you agree with 4 of them without question. So let us discuss the remaining 11 points, as listed above.
2. I would suggest that we do a structured discussion, or eat the big elephant bite by bite, so make the discussion not getting too complicated.
3. I suggest to limit/confine/qualify the topic on the input side, because this the part that causes all the trouble and controversy.
4. Now let us start with your Point 1 - I agree that it is might not be a good idea to use or buy jumper set Low Level trigger. So for now we will only talk about High Level trigger relays. So we can put aside your Point 1. But see update 1 below.
5. Your Points 2, 3 - I agree with you that we need to make sure if the input voltage at Vin drives the LED in the optocoupler into (a) inactive, (b), active, (c) fully saturated state. I will later look at the spec and do some calculation and see if you agree or not.
6. Your Points 4, 5 - We need to make sure if the Rpi, Arduino, or anything that, because using High Level trigger mode, acts as a source driver, drives, within a safe limit, a current through the the LED to ground. I can calculate/experiment to find out.
7. Your Points 6, 7 - We also need to make sure if the Rpi or Arduino's driving current is not big enough to damage the LED. I can calculate/experiment to found out.
8. Your Points 8, 7 - We need to make sure if the logical power Vcc driving the LED, or the JdVcc driving the coil, is not too big to damage the LED, or the coil. I agree, we need to make sure that.
9. Your Points 9, 10 - We need to make sure the whole system (input side with the optocoupler, output side with coil and driving transistor, biasing resistor etc) operates in the safe region.
I agree with all your points above. So I will refine my original 15 points, take consideration of your concerns, and make a Version 2.
I suggest that we do a casual discussion, but keep strict principles (Ohm's Law, LED and BJT characteristics etc). So we won't have any deadline, or insist on reaching a yes or no conclusion.
There is a chance that after discussion, we will agree that we disagree.
No hurry to reply. Think and take your time. I am thinking aloud, so there should be many typo mistakes or unstructured things. My apologies.
Update 1 - 2018aug22hkt2042
I once said I always prefer Low level trigger, for a reason. That is, I almost never use Rpi GPIO to directly (source or sink) drive a relay, no matter the relay input side is an optocoupler or BJT only. I almost always use some sort of Logical Lever Converter.
In other words, if I can use a level shifter, then I prefer Low level trigger.
But since our discussion is on how newbies should buy or use relays. We should not expect or insist newbies to buy an assembled level shifter or solder 2N2222, ULN2803 etc.
So for our discussion here, without using level shifter, I agree that it is a bad idea using Low level trigger, using Rpi as a sink driver.