David Szpunar: Lead Engineer, PC Help Services

David's Church Information Technology

June 29th, 2007 at 3:45 pm Print This Post Print This Post

Proximity Card Readers, Parent Pager, and AC/DC Power Adapters Adventure

We use proximity (“prox”) card readers with our Parent Pager Plus system to assign pagers (and optionally assign a prox card to each family) for sign in and emergency contact purposes. When we added a check-in station several months ago, we purchased a used prox card reader but received no power plug for it. So it’s been sitting unused while we used that station as an administrative station, but we need it to work now for reasons I’ll spare you.

In the past, we had one of our prox reader plugs fail, and I was able to replace the failed plug with a generic Radio Shack plug that worked fine. It was a Radio Shack model 273-1773 adapter, and it provides 12V output up to 500mA. The original plug provides 12V output up to 300mA, so that model should have and did more than do the job. Radio Shack has apparently updated their adapter product line in the year or years since I purchased that unit, and now they have a new model number, 273-1774, that’s a bit smaller and lighter, but looks the same and has the exact same output specifications (up to 500mA). I purchased two of them, so we’d have a backup, and even tried plugging in the prox reader I took to the store before I left and sure enough the power light came on!

That was last night on my way home. Today, I go to plug in the adapter, and the power light comes on on the prox reader but it won’t scan (it beeps upon successful scan, and it won’t beep and won’t output to the computer). We have several readers, so I mixed and matched adapters (and interchangeable tips even), and the readers all worked no matter what (even on the old Radio Shack adapter with the exact same adapter tip) — unless they were plugged into either of the new adapters, when they didn’t work.

Why? I don’t know. If you do, let me know! There’s no logical reason why the new adapters shouldn’t work just fine.

There is happy ending. I returned to Radio Shack and was able to test their 3-12V adjustable AC-to-DC adapter, with up to 1000mA (1A), model number 273-029 (the box says 273-0029, the adapter and website say 273-029, and a search of their website using either brings up the right unit). These adapters cost only $0.85 more each, and they work perfectly fine, with the same adapter tips. Other than a wasted two hours and 10 mile round-trip for the exchange, the fix wasn’t too bad and it’s still going to be functional by Sunday. But I still have no idea why the adapters that didn’t work, didn’t work! The salesman when I exchanged them even tested one of them to make sure they were providing 12V. And like I said, I had two identical adapters that both refused to function properly! The mystery remains…