Can I use 3.3v output of w7500 to control 8-channel relay boards developed for arduino 5v otput?

Question

Hello to all I have found a lot of 8-chanel relay modules on the aliexpress. Red boards are controlled by positive signal, blue boards by negative. Relay needs more energy then output of most controllers, so relays has own power (can be 3.3, 5, 12 or 24v). To control relay by controller optocupers are used. These boards are developed for use with 5v arduino output. I want to use with 3.3v output of w7500 board. But I can not found in docs - what optocuper are used there? Can I use it with 3.3v? What is minimal voltage to open optocuper? I reviewed boards datasheets but there is no any info about used optocupers and minimal signal level. Project details: relays are powered by automobile battery (12~14v) relays should be controlled by 3.3v of w7500 output relays load can be any, 220v for example. It is custom alarm system. Car battery (used) is a big power bank) It shoul open electromagnetic lock or actuator if someone cut main 220v line. Thank you. Sorry for my English)

irina · Answer

Hi~ Yegors I’m so sorry about getting back to you so late. First, I think you use the 3.3v and 5v as output voltage using the wizwiki-7500. See J13 on the wizwki-w7500, you can see the 3.3v and 5v pin. And I don’t know what “optocuper” is. I think it’s like the LED or something, is it right? YegorS: . I want to use with 3.3v output of w7500 board. But I can not found in docs - what optocuper are used there? Can I use it with 3.3v? What is minimal voltage to open optocuper? Tell me more about the optocuper. thanks, BR

YegorS · Answer

Hello Irina Kim Tell me more about the optocuper. It is syntax mistake. I mean “optocoupler”. It is used for electrical isolation.

YegorS · Answer

Hi I am new in mbed and microcontrollers programming. On the different forums I found solution - how to connect more then 3.3v devices directly to microcontroller: need to enable “open drain” mode and disable pull-up resistor. It lets to control devices which use more then 3.3v, for example 12v. Disabling the resistor prevents the board from burning out. My questions is: what max current for each IO pin can I use in this mode? (Open drain with disabled pull up) what is max voltage can be used in this mode? (Max collector junction breakdown voltage) what is max sum current can be used for all pins at same time? Example of code: https://os.mbed.com/teams/TVZ-Mechatronics-Team/wiki/Digital-inputs-and-outputs https://community.st.com/s/question/0D50X00009XkXlk/can-5-v-tolerant-pin-be-turned-off Thank you.