Alternate transistors for BS1 serial adapter?

DigitalMan

I'm rather new to working with components, or at least too new to trust my judgement, so I figured I'd double-check before my assumptions break something.

I have neither 3906 nor 3904 transistors. What I do have is a shiny new PNP from Radio Shack and three working·NPN's desoldered from RC car remotes. How picky is the serial adapter schematic? Can I get away with using any old transistors, as long as they can handle the current and voltage?

I also see a lot in schematics online, such as one for·a PIC programmer (another important circuit I'd rather not screw up), that I'm allowed to use "equivalent" transistors to the ones shown. What does that mean? Are there specific values in the spec sheets I should be comparing?

I apologize if these are stupid questions, my web searching found nothing on this matter.

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;Long live the SX18AC/DP!

PJAllen

· 2N3904, -3906 are general-purpose amplifier and switching transistors.· It could well be that the parts you propose will suffice.·
· The schematic is definitely "picky" such that the electrodes of the transistors have to be got right.· So, you need to pin out your transistors -- because sometimes they're E-B-C and sometimes they're E-C-B.
· Especially in the case of these R/C pieces.· What sort are they, do you have datasheets?· The more you know, the less likelihood of your making an "did I fry my stamp? please help" post (replete with cry-baby emoticon.)

DigitalMan

Fortunately, I do know to make sure the pinouts are right.

The PNP MPS2907 from Radio Shack is just that, a general purpose switching and amplifier transistor. I've got the package with the pinout.

The 1815 is described differently depending on who makes it: http://www.datasheetcatalog.com/datasheets_pdf/1/8/1/5/1815.shtml·Two out of three say it's general purpose, will that do?

The C1213 (presumed to be 2SC1213, http://www.datasheetcatalog.com/datasheets_pdf/2/S/C/1/2SC1213.shtml·) appears to be just a low power amplifier. I intended to use two of these, should they be swapped out? In a test circuit with a button and an LED it works as one would expect, but a serial adapter is a bit different from a little light.

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;Long live the SX18AC/DP!

Post Edited (DigitalMan) : 6/22/2006 12:16:45 PM GMT

PJAllen

Provided you get everything right (E, B, C -wise), then it'll likely work out, at least it shouldn't result in a catastrophe.

Beau Schwabe

For a quick way of determining EBC of a transistor, I usually throw together a simple
circuit that looks like the one below and do the "wet-finger" test.

           NPN
                     LED     1K
GND >-----E B C------->|----/\/\----o----< +9V
            |                       |
            |                       |
            |                       o----<
            |               10K            Touch here
            o---------------/\/\---------<

Note: For a PNP just reverse the battery polarity and the LED polarity.




PS) Why not just buy a 15 pack of NPN or PNP transistors from RS?

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

DigitalMan

Whoa, how bizarre. Radio Shack actually carries the 3904, that's the first time they've ever carried any specific part I needed beyond resistors. I have mountains of transistors coming in from eBay, so I just got the three I needed now (I'll save my desoldered pieces for when I just need to turn on an LED or something).

And in another bizarre twist of events, the thing actually works! It isn't pretty, but it does the job just fine. And it is actually the first circuit I've ever assembled, that had any use anyways.

Thanks for the help!

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;Long live the SX18AC/DP!