user53994: I have a problem similar to these questions:
Wemos D1 doesnt drive Relay
Wemos D1 is not triggering Relay
I got this BC548B transistor from an old apparatus I scratched. The transistor saturation voltage is 0.6V  according to the datasheet:
https://alltransistors.com/pdfdatasheet_fairchild_semi/bc548_bc548a_bc548b_bc548c.pdf
When I set up my circuit the wemos d1 inboard leds dim and the board resets so I guess something is going really wrong. Can someone advise if my design makes sense?

UPDATE
I replaced the 12V relay with a 5V one but still can't get it to work. Basically, the 3.3V signal seems to be too low to activate the solenoid. How can I raise the 3V3 signal to 5V? What was wrong with my idea of using a transistor to do it?


user2967: That appears to be a 12 "solid state" relay. That means that it is designed to be both powered by and switched by 12V. You're trying to drive it with slightly more than 1/3 of its rated voltage. Don't do that.
Edit:
Note that none of the relays being discussed are true solid state relays. These are are all conventional coil relays that include cicuitry that allows them to be driven by CMOS logic signals. A true solid state relay does not have any moving parts, but uses solid state components to do the job of a relay. Those cost significantly more money however.)

It might be that you can get away with driving a 5V solid state relay with 3.3V, or 12V relay with 5V, but you shouldn't do those things either.
Also note that even if you are using the correct relay, your relay almost certainly takes more current than the 5V pin on an Arduino can provide (When driven from USB, the entire system is limited to 500 mA, including the power needed to the Arduino.)
Edit:
These solid state relays come in 12V, 5V, and 3V flavors. Get a 3V one: https://www.adafruit.com/product/3191?gclid=EAIaIQobChMIyY_dxM344gIVELbICh1ufwivEAQYBSABEgI3wPD_BwE

53994: <p>I have a problem similar to these questions:</p>

<p><a href="https://arduino.stackexchange.com/questions/52945/wemos-d1-doesnt-drive-relay">Wemos D1 doesnt drive Relay</a></p>

<p><a href="https://arduino.stackexchange.com/questions/65941/wemos-d1-is-not-triggering-relay">Wemos D1 is not triggering Relay</a></p>

<p>I got this BC548B transistor from an old apparatus I scratched. The transistor saturation voltage is 0.6V  according to the datasheet:</p>

<p><a href="https://alltransistors.com/pdfdatasheet_fairchild_semi/bc548_bc548a_bc548b_bc548c.pdf" rel="nofollow noreferrer">https://alltransistors.com/pdfdatasheet_fairchild_semi/bc548_bc548a_bc548b_bc548c.pdf</a></p>

<p>When I set up my circuit the wemos d1 inboard leds dim and the board resets so I guess something is going really wrong. Can someone advise if my design makes sense?</p>

<p><a href="https://i.stack.imgur.com/zA0i3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zA0i3.png" alt="enter image description here"></a></p>

<h1>UPDATE</h1>

<p>I replaced the 12V relay with a 5V one but still can't get it to work. Basically, the 3.3V signal seems to be too low to activate the solenoid. How can I raise the 3V3 signal to 5V? What was wrong with my idea of using a transistor to do it?</p>

<p><a href="https://i.stack.imgur.com/WqbGB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WqbGB.png" alt="enter image description here"></a></p>
 2967: <p>That appears to be a 12 &quot;solid state&quot; relay. That means that it is designed to be both powered by and switched by 12V. You're trying to drive it with slightly more than 1/3 of its rated voltage. Don't do that.</p>
<h2>Edit:</h2>
<p>Note that none of the relays being discussed are true solid state relays. These are are all conventional coil relays that include cicuitry that allows them to be driven by CMOS logic signals. A true solid state relay does not have any moving parts, but uses solid state components to do the job of a relay. Those cost significantly more money however.)</p>
<hr />
<p>It might be that you can get away with driving a 5V solid state relay with 3.3V, or 12V relay with 5V, but you shouldn't do those things either.</p>
<p>Also note that even if you are using the correct relay, your relay almost certainly takes more current than the 5V pin on an Arduino can provide (When driven from USB, the entire system is limited to 500 mA, including the power needed to the Arduino.)</p>
<h2>Edit:</h2>
<p>These solid state relays come in 12V, 5V, and 3V flavors. Get a 3V one: <a href="https://www.adafruit.com/product/3191?gclid=EAIaIQobChMIyY_dxM344gIVELbICh1ufwivEAQYBSABEgI3wPD_BwE" rel="nofollow noreferrer">https://www.adafruit.com/product/3191?gclid=EAIaIQobChMIyY_dxM344gIVELbICh1ufwivEAQYBSABEgI3wPD_BwE</a></p>
