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Replace relays with solid state circuit

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Hi Eric,
Is there any special reason to use 2N2222 instead of ZTX450 (or other NPN) at the "Select" point in the circuits? I think I either got a bad batch of 2N2222's or they are more sensitive to heat when soldering and I'm frying them. Do you recommend using crocodile clip when soldering transistors?
 
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Hi Eric,
Is there any special reason to use 2N2222 instead of ZTX450 (or other NPN) at the "Select" point in the circuits? I think I either got a bad batch of 2N2222's or they are more sensitive to heat when soldering and I'm frying them. Do you recommend using crocodile clip when soldering transistors?

Hi,
No special reason for the select 'except' for I would use a ZTX to drive the 330R to the TIP, even though a 2N2222 would do the job.

The 2N2222 is only passing a few milliamps so they should not fry.

Check that you are connecting the 2N2222 pins correctly. look at this image.

I never use a cooling clip when soldering transistors.
What type of solder iron are you using.?
 

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The 2N2222A I am using has a TO-18 case (datasheet attached). The one in your picture has a TO-92 case.

I am using Weller soldering station with digital temp control set to 600ºF. I don't think I've fried any of the ZTX's but maybe have on the 2N2222A's.

The leads on the 2N2222A are flimsy so I'll use ZTX450's for all the NPN's and ZTX751's for all the PNP's (except where I need the TIP32), OK?

I have components setup up with 4 displays on breadboard just as you have described in Hiker7.pdf. All is working fine. :) Just for fun I tried to use the ULN2803 circuit in place of TypeB and could not get it to work. I think it's something to do with sharing a common input junction with 2 ULN's. So I'll stick with your circuit without the ULN.

Next, I'll test your circuit here that I will substitute for TypeB and keep a constant +5v on the green anodes. That will be less components and work but I'll need to test to see if there are any complications from having +5v on both anodes at the same time.
 

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