Now I have checked the LED current vs Vin from 0V to 5V, to make sure that the trigger band is not too narrow to cause a stability problem. The engineering trade off / experimentation is selfied below. So I did a couple of trials and errors and found 4k7 seems a good choice. So just increase the current limiting resistor so that the current is below 0.15mA when Vin ~=3V (or 2.8V, to add a little bit of safety margin).īut if modified current limiting resistor too large, then photo transistor won't saturate. The trick is to note that the corresponding trigger current is around 0.15mA (highlighted in orange).
I need to modify the circuit so that the trigger band shifts down to below 3V, Rpi's High signal value.Īctually it is very easy to shift the trigger band down to below 3V. Now I can see the trigger point is 3.84V (off). To look at the whole picture of the relay characteristics, I used a adjustable voltage power supply to check the If vs In voltage, and plot a graph as below. To make the relay 3V3 logic or Rpi compatible, the 3V3 current should be so small to cut off the optocoupler and therefore relay off. Now that for the fixed input values of oV, 3V3, and 5V, the currents are 3.8mA, 0.6mA, and 0.002mA, and corresponding status of relay are On, On, Off. I checked that the IN current at 0V = 3.8mA, at 5V = 0.001mA, but at 3V3, current is still high, 0.6mA. This means 3V3 is not high enough to switch off. Howeve, Green LED is still on if IN = 3V3.
Green LED is on if IN = 0V (Gnd), off if IN = 5V. Now I am using a jumper wire to connect IN to the following voltage levels, (1) Ground, (2) 5V, (3) 3V3. Now a picture of the real thing - the OP's relay and two similar relays I am testing. There are 5 methods to get around, and a schematic is helpful to explain. However, 3V3 Rpi's low signal meets spec, but high signal is only around 3V, therefore cannot switch off the relay. This type of relay switches on if input signal is less than 1V, and switches off when input is greater than 4V.Īrduino has no problem because its high low signal meets the spec. The OP's relay is optoisolated, low level triggered designed for 5V Arduino. If 4k7 does not work, read the long answer below to find a value that works. Rpi should now switch on/off the relay without any problem. Solution 1 - Add a resistor at the input terminalĪdd a 4k7 resistor at the IN terminal. Only the relay status led is getting blinking, but not the relay switching sound is not being heard. (No power supply is there from the Raspberry Pi). The new part numbers are OPI104-HS-DIN and OPI104-HS-FT.Do keep in mind that I have used the Raspberry Pi for only GPIO pins connection to IN1 and IN2 of the relay module and power supply to the relay module is from that breadboard power supply module I have put the link to above.ġ) JD-VCC of the relay module to 5V of the power supply module.Ģ) VCC of the relay module to 3.3V of the power supply module.ģ) GND of the relay module to the ground of the power supply module.Ĥ) IN1 and IN2 of the relay module to Raspberry Pi's GPIO 13 and GPIO 6 pins. Standard output stage, and whose switching speeds are much faster. Due to present supply chain delays for the protected output stage components, we have introduced a new variant which uses a Speeds are slower due to the protection circuitry. The original OPI104 variant (OPI104-DIN, OPI104-FT) utilizes an output stage which includes current limit and thermal limit features, but whose output switching
#Optical isolator for raspberry pi 3 driver#
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