[TriEmbed] One final question regarding my solenoid project

Pete Soper pete at soper.us
Sun Nov 3 19:50:52 CST 2013


I think we should look at this circuit again. The intent is for 
(*output*) pin "IN0" to be pulled to ground to allow current to flow 
through the optoisolator and the LED, coupling light into the 
phototransister to turn on Q1 and pull in the relay (which presumably 
supplies current to the solenoid). When the pin is driven high the 
current flow stops and the output pin is looking into the high 
resistance of the LED.

But this is annoyingly complex, and now you need a third power supply 
voltage.

Instead I think one MOSFET and one rectifier will get the job done. 
Here's an example of a MOSFET driving a solenoid. The MOSFET Adafruit 
sells has a max on threshold of 2.5 volts, so a Raspberry Pi gate should 
turn it on just fine.

    http://learn.adafruit.com/biometric-security-box
    (solenoid circuit at 
http://learn.adafruit.com/biometric-security-box/circuitry )

-Pete




On 11/3/2013 5:10 PM, Scott Hall wrote:
> Excellent catch for newby.  It is by no means the only way to approach 
> the problem, but a very effective one.
>
> The 2mA draw of the LED in the optoisolator is well within the GPIO 
> pin specs of the Raspberry Pi.
>
> However make sure that you use a separate 5V supply to power the relay 
> board, but you can power the opto- LED from the R'Pi's 3.3V power if 
> you use a 470ohm resister (R1) instead and forgo the extra LED (IN1), 
> or use a 120ohm resister if you keep the extra LED.
>
> On 11/03/2013 08:53 AM, Lucas Rumney wrote:
>> I am sorry to email the group yet again for the same project, but I 
>> have been doing research and I wanted to know if there would be any 
>> issues with using these parts together, and if they could be put 
>> together into a circuit that would actually protect the pi, and 
>> control the solenoid with the pi (I am a real noob at this, but I 
>> don't intend to be for long)?
>>
>>
>> would this optoisolated relay board cover all of the parts I need, 
>> and be in the correct range (safe fore the raspberry pi, and also 
>> usable with the solenoid linked later in the email?)
>> http://yourduino.com/sunshop2/index.php?l=product_detail&p=218
>>
>> solenoid:
>> http://www.adafruit.com/products/413#Technical_Details
>>
>> I have read up on the relay board, but I don't understand all of the 
>> stats, and I dont want an imcompatability to ruin my pi.
>>
>> Thank you guys for being so helpful, I've been trying to get this 
>> done in between work and school.
>>
>> Lucas
>>
>>
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>
>
> -- 
> Scott G. Hall
> Raleigh, NC, USA
> ScottGHall1 at GMail.Com
>
>
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