relay selection

pwdixon

Joined Oct 11, 2012
488
Looks like it would be perfectly fine.
By the way for a better datasheet look up the part on the CPC companion site farnell.
 

MaxHeadRoom

Joined Jul 18, 2013
19,058
Is it imperative that you need isolation, I have used the ULN2803 or single 2n7000 for many low voltage systems with no problem.
This eliminates the need for any opto etc.
Max.
 

Thread Starter

duxbuz

Joined Feb 23, 2014
133
Is it imperative that you need isolation, I have used the ULN2803 or single 2n7000 for many low voltage systems with no problem.
This eliminates the need for any opto etc.
Max.
Sorry Max I missed the context of your post.

You mean isolation for motor control?
 

MaxHeadRoom

Joined Jul 18, 2013
19,058
Isolation to the relay, which in itself provides the motor isolation.
IOW, do you really need the opto?
I usually operate the relay direct by either 2n7000 or if more than one, ULN2803.
Max.
 

Thread Starter

duxbuz

Joined Feb 23, 2014
133
Well as a novice this circuit isolation is proving to be blinking hard work. ha ha.

I have these parts. I also have a relay and an optocoupler. http://cpc.farnell.com/stmicroelectronics/uln2003a/darlington-array-7npn-2003-dip16/dp/SC08601?Ntt=sc08601

http://cpc.farnell.com/on-semiconductor/mps2222a/transistor-npn-to-92/dp/SC06675?Ntt=sc06675

http://cpc.farnell.com/on-semiconductor/p2n2222ag/transistor-npn-to-92/dp/SC12549?Ntt=sc12549

I thought I was just going to wire up a relay. I have seen lots of youtube videos with people using transistors. But now I realise there are obviously gazillions of different transistors. Mosfetts, npn(hundreds of these) and some people use 2.

A way to go yet.

Not to be unappreciative of any advice. Just laughing at my naivety. :D
 

MaxHeadRoom

Joined Jul 18, 2013
19,058
It is just another way to look at doing almost the same thing, except it shows using 3 components instead of 8!
1-2n7000, 1-relay, 1-diode.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
19,058
None exactly, your original circuit achieves virtually the same thing with two stages of isolation and a few more components.
In any small low power project I look to the Fet approach before a bi-polar one if possible.
I always keep a stock of 2n7000's on hand for that reason.
Max.
 

pwdixon

Joined Oct 11, 2012
488
I think I missed the point of this whole thread, I had assumed this was a learning experience and that it didn't matter what the circuit was really it was just to learn about the components and how they work etc.

Are you trying to achieve a real outcome other than just learning?

If you are then we might need to know what you are actually trying to achieve overall.
 

Thread Starter

duxbuz

Joined Feb 23, 2014
133
I have forgotten the point of the whole thread! I have forgotten which thread it is!:D

I think this is the thread that I am trying work out what to use to create a circuit using an arduino a small lego motor and a 9v battery. without frying the arduino!

The relay idea seems to have gone out the window in favour of LL mosfet or bipolar transistor like a TIP120.

These seem simpler circuits with less moving parts :)

Thanks for your patience. I have tested everyone's I feel
 
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