resistor values for 2n2222a w/ SSR

[evilkitty]

Re: resistor values for 2n2222a w/ SSR

Thanks, now i know what resistor to use for my DIY smart light socket

Now as for that dual relay setup, i want to emulate the logic of my mechanical relay (SPDT)

PNP and NPN transistors have opposite switching characteristics

i have access to my data pin, 3.3v, 5v, and ground and very little pcb space

[redwire]

Re: resistor values for 2n2222a w/ SSR

The Omron G3MB-202P DC5 relay is an SSR, which is basically an LED and 440Ω resistor inside (for the 5V model) and roughly around 10mA load.
With a lazy 2N2222 beta of 75, base-drive 2.6kΩ or lower would be plenty, and 1kΩ is fine. The RP2040 GPI/O's output 3.3V and typ. 4mA but note their are settings gpio_set_drive_strength can also move it from 2,4,8,12mA in software.
You need an NPN to keep the higher SSR voltage away from the RP2040.

[eccerr0r]

Re: resistor values for 2n2222a w/ SSR

It looks you're just using common ground level shifting you need NPN transistors and the PNP probably is not useful here if you can't get the shifted voltage elsewhere.

Since the relay is only 7.5mA (and will be even less current with the 30ft wire plus transistor saturation voltage) you don't need to current limit collector, and you don't need much base current to keep the driving transistor on. A 1K base resistor should be sufficient for even weak 2n2222a's and you can do 470Ω if you want to pound the transistor even more.

[evilkitty]

Re: resistor values for 2n2222a w/ SSR

The relay pulls 7.5mA when wired to my usb port, so what resistor range/value be?

i know there is a formula, but i am not sure what values to use


note that my final circuit will be using 5.2-5.35v, however there will be around 25-30 ft of telephone wire to the relay

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as for the second part of the question, it seems i have 2N3906 for PNP, would (would have issue with a double on for state for a moment?) this work see attachment
maybe i need a schottky diode on the PNP base?

again not sure what resistor value to use

[stj]

Re: resistor values for 2n2222a w/ SSR

a PIR sensor on the ceiling works well btw, i have done it on a staircase once

[stj]

Re: resistor values for 2n2222a w/ SSR

most ssr's use an optocoupler and can run down to 3v
to answer the question, you need to find out how much current the ssr needs, then look at the 2n2222 hfe and then you can calculate the current.
ir just experiment starting with 10k

[evilkitty]

So if I take a 2N2222A transistor and a G3MB-202P relay and 3.3v logic controller

What resistor value should I be using for the base? Normally i would just take a ~1k resistor and go, but i need to work every time and not fail

The problem I am trying to solve: my dad hates 3 way switches (he is not even the one wiring them) and insist on the only way to get through a room at night is to turn the light on, go to the other side of the room and turn that light on, go back and turn the 1st light off, then go back again and turn that light off, screw that I'll make a software light switch that uses door sensors (more reliable than a motion sensor working)

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second question if i use the same logic wire can i make a double throw SSR switch by using 2 of these one on a 2N2222A and a P2N2222A or would i have issues with overlap there both are on/off at the same time (not sure if that is even a issue for my thermostat)