Need hardware advice: ULN2003A

[Christopher4187]

Luciano,

Thanks for pointing out the pin 9. I setup one of my alarms to cycle the relays every second and I measured the voltage when the field collapses. Based upon what we discussed here, I should have expected this. The voltage when the field collapses is 64 volts but when pin 9 is connected, it is only 12.5 volts. Of the 90 units I have in the field, none of them have pin 9 connected. I guess it is not a matter of if but when they will fail.

I will let this test alarm cycle until the ULN2003A fails. At least I will have an idea when I should expect them be returned for warranty repair. Also, I will post when the ULN2003A fails if anyone is curious. If there is anything positive to come out of this, at least I caught the issue now with 90 alarms in service as opposed to 1000 alarms in service.

Thanks again for pointing that out. You probably saved me a lot of headaches wondering why my alarms are going to fail in the future!

[Luciano]

Hi,

Some interesting stuff.

http://www.circuitcellar.com/library...9/c99cdpdf.pdf
http://www.circuitcellar.com/library.../c109cdpdf.pdf
http://www.circuitcellar.com/library...99/c1299cd.pdf

(In the first link they talk about the ULN2003A).

Best regards,

Luciano

[Christopher4187]

Thanks for the info. I actually read this yesterday when doing a search on the ULN2003. My test alarm has been cycling on and off for over 21 hours and has simulated 11 years (26,000 cycles) of operation. The ULN2003 and the relays are still working great; it's not what I would have expected without connecting pin number 9.