Can I make my relays high rather than low? - Page 1
Forum section: electronics / beginners

author: billbyrd1945
author_rank: Regular Contributor
timestamp: March 29, 2019, 11:37:11 pm
content: I have an eight-relay module. The relays are activated when their input pin is taken low. Is there some way to make the relays respond to a high signal? Photos attached. Thank you.

author: langwadt
author_rank: Super Contributor
timestamp: March 29, 2019, 11:52:24 pm
content: Quote from: billbyrd1945 on March 29, 2019, 11:37:11 pmnot with out some bodge wires

author: digsys
author_rank: Unknown
timestamp: March 30, 2019, 12:07:09 am
content: A quick search find this -http://wiki.sunfounder.cc/index.php?title=8_Channel_5V_Relay_Module1x resistor + 1 Led on the opto. Moving 1 end each will do what you want ieConnector > resistor > OptoAOptoK > LedA > GND

author: Gregg
author_rank: Super Contributor
timestamp: March 30, 2019, 05:40:13 pm
content: Look for relay modules that have high/low triggering jumpers like this:https://www.ebay.com/itm/1PCS-DC-5V-8-Channel-8CH-Relay-Module-with-Optocoupler-isolation-H-L-high-lo/173673557254Use search terms in fleabay like: 5v high/low relay 5v h/l relayNote the pictures of the modules to make sure they have jumpers to change high or low trigger (they are yellow on the one shown)

author: Ian.M
author_rank: Super Contributor
timestamp: March 30, 2019, 06:38:25 pm
content: The O.P's one is yet another crappy chinese relay board. Optoisolation is fairly pointless if there's a common ground. I'd also give 50% odds there's insufficient creepage/clearance distance to use it for mains, and that the relays can't actually handle 10A. You are pushing your luck if you use it for over 50V AC or over about 15V DC or over 3A!The one at Gregg's EBAY link looks reasonably nice - the PCB is slotted to increase the creepage distance of the common terminal of each relay. Unfortunately it looks like the ground plane gets too close to the end of the slot so some surgery with an Xacto knife to trim the corners of the ground plane copper at the slots may be required if you want to use it for 230V AC.It does however over-complicate things with jumpers as all such a relay board needs is two separate connections to the input side of each opto, so you can freely choose whether to drive each channel common anode, or common cathode simply by how you wire the inputs.Probably the easiest fix for the O.P. without replacing the relay board would be to use a74HC540inverting octal buffer between their signal source and the existing relay board inputs, with both its enable inuts tied low.

author: Gregg
author_rank: Super Contributor
timestamp: March 30, 2019, 08:02:01 pm
content: The Chinese opto hogh / low modules are so cheap that it probably is easiest to just buy the correct ones.The high / low modules are actually quite useful for situations where a real contact closure is desired. They can be wired to totally isolate the signal from the relay coil power by using the VCC and the center pin of the jumper. I use a DuPont 3 position socket with only the center wire installed so it can’t be mixed up.Changing the resistance to the opto isolator by either replacing the one on the board or another in series with the signal allows use of different signal and coil voltages. For instance a 12V coil module can be triggered by an Arduino 5 volt signal.Enclosed is a picture with notes I made for a friend when I used some of these for his shop alarm. The alarm board has a very limited switching power capacity.