I was designing a circuit to manipulate in's and out's in a car.

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I use a step down converter to power up the Arduino.

The inputs, in the left of the Arduino are:

  • GIN : General grounded Input.
  • JAMIN: Is a grounded signal.
  • DOORIN: Is a door sensor and grounded signal.
  • 1-WIREIN: Is an Ibutton reader.

The outputs, in the right of the Arduino are:

  • 1-WIREOUT: Arduino acting as a 1-wire slave.
  • GOUT: General grounded Output.
  • JAMOUT: It is connect to the relay ground wire to activate it.

The JAMOUT pin does not work. Maybe the current of the optocoupler is too low. I measure the base-emiter voltage and it gives -1.23[V], i think this is why the transistor is not switching on. Can somebody tell me if there anything wrong with my circuit.

  • \$\begingroup\$ LM2596 is a switching regulator, you need quite a few more components to make it work right. You need an input capacitor and output capacitor(s), along with a diode and an inductor, unless what you show is a module based on the LM2596? \$\endgroup\$ – Ron Beyer Nov 22 '17 at 17:14
  • \$\begingroup\$ Yes , is the module. \$\endgroup\$ – Arturo Veras Nov 22 '17 at 17:37
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    \$\begingroup\$ I'm voting to close this question because it's dormant \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 27 '19 at 22:18

LM2596 is a switching regulator, as Ron Beyer says, so you'll need to add an inductor and the return diode as well as an output capacitor (as on page one of the datasheet). It would be good practice to add input capacitors.

A decoupler on the micro will also be needed, unless there something included with the one you're using?

Why do you have 1ks on the LEDs of the opto-couplers? Would have thought that 100R would have been closer to the mark? (Depending on the current requirement of the opto).

Assuming that all your input pins are pulled up in the microcontroller, and the outputs are all strong enough to drive the LEDs in your opto-couplers, they should be ok.

One word of warning; automotive power rails are horrendously awful in terms of regulation and spike etc. I have designed input circuitry for automotive supplies and can tell you it takes a lot to smooth it out to something reliable. If this is just a quick home project, you may get away with just some basic large input capacitor, but I wouldn't be surprised if you blew a collection of the converters.

  • \$\begingroup\$ The Arduino in this schematic also looks like a "module" decoupling included. Also I'm not sure what the diodes on the input lines are doing. I, for example, don't see anything inductive going on here, so they seem gratuitous. \$\endgroup\$ – vicatcu Nov 22 '17 at 17:42
  • \$\begingroup\$ @vicatcu , do you mean D1, D2 and D3? \$\endgroup\$ – Arturo Veras Nov 22 '17 at 18:10
  • \$\begingroup\$ @Puffafish, Why do you have 1ks on the LEDs of the opto-couplers? The 1k resistor is for limiting the current. The datasheet says that optocoupler máx current is 50 [mA] Would have thought that 100R would have been closer to the mark? With 100R the simulation says that is 36 [mA], i think is too close to the maximun. \$\endgroup\$ – Arturo Veras Nov 22 '17 at 18:28
  • \$\begingroup\$ @ArturoVeras ya... D4, D5 and D6 for that matter. I don't think they are particularly useful in this application. And the 100R vs 1k question is a tradeoff, but I would try to design for at least 10mA going through the LEDs. \$\endgroup\$ – vicatcu Nov 22 '17 at 18:35
  • \$\begingroup\$ @vicatcu, I think you are right about D4, D5 and D6. \$\endgroup\$ – Arturo Veras Nov 22 '17 at 18:45

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