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Driving relay shield directly from ESP8266 3.3V ?
Posted:
Fri Jul 07, 2017 4:42 pmby hary
Hi.
Well, the question is almost already all in the title.
I wonder if the 3.3V from ESP8266's GPIO would be able to drive directly a relay shield like this one :
http://www.ebay.fr/itm/5V-4-Channel-Rel ... Sw3utY7wk4In fact, the ESP8226 has only to drive the first stage which is a LED from the Opto-isolator.
Has anybody tried it before to say if it need a level shifter or not ?
Re: Driving relay shield directly from ESP8266 3.3V ?
Posted:
Fri Jul 07, 2017 9:10 pmby rudy
The listing says the requirement for the optocoupler is 15-20mA. The max for the ESP8266 is 12mA. If it would work it might be marginal.
Re: Driving relay shield directly from ESP8266 3.3V ?
Posted:
Fri Jul 07, 2017 9:12 pmby Anthony420
Not that Chinese Ebay specifications can be trusted, but the listing indicates 15 - 20 mA drive current per channel. That would suggest you need to buffer the outputs.
Not sure if you can do it here, but for some FET LED drive amplifiers i've been successful changing the SMD resistors / Zeners on the opto isolator input circuit to drive reliably from low current 3.3V. Just a thought but worth looking at because 15mA sounds high for an opto isolator input to me.
Anthony
Re: Driving relay shield directly from ESP8266 3.3V ?
Posted:
Sat Jul 08, 2017 5:51 amby btidey
The spec sounds a bit dodgy to me for the drive current if that is referring to the logic input. Typically modules like this need less than 4mA to activate.
Unfortunately most of these relay modules are poorly described with respect to their input requirements (active high/low, drive voltage/current). Most like this one also use optocouplers but wired in a way that does not give any significant extra isolation.