Unknown SMD Component in barcode wand

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Hi Guyzz

I just got a barcode wand (Metal Pen) , unknown model

It has a DB9-Female , and if you take it apart there is 3 wires going to the PCB.

Black = DB9 Pin7
Red = DB9 Pin 2
Orange = DB9 Pin9

There was an Electrolytoc Cap (10uF 25v) , and from tracing the wires that one i could figure out that :

Black = Ground
Orange = +
Then Red must be Output i guess (i suppose TTL).

Well i hooked it up to +5v and connected my scope on the Red data pin and to ground , the scope is "quiet" when there is power on the pen (straight line on Zero volts) , there is a bit of noise when i remove power from the wand.

I got light in the pen , and did a swipe ...... Nothing happened on the scope.

Adjusted the scope to 500mv and 500ns , and got some reaction , but the level is absolutely not TTL , its maybe 50..100 mv.

There is a smd component marked Q1 on the PCB , it has same size as a BC850 (a BC547 SMD variant). Is the house called SO-23 it has got 3 legs , two in the bottom and ine in the middle on the opposite side.

The ligth pen part of the PCB is encapsulated in some kind of copper foil , and sealed. And out of that part comes a PCB trace that goes to a potmeter , and from that one it seems like it goes to Q1 , the left leg. Q1 the right leg goes to ground , and the leg in the middle goes to the Red wire (The output)

To me it looks like it is generating something on the scope , i get some small wawes (100mv or less, but it reacts when i swipe across some black and white text).

Q1 has the below marking 1AM and a symbol that looks like this >-|

Quote:

1AM>-|

1: Should i try with more than 5v ??
Could it be for +12v , and output RS-232 (i would prob not put my money on that one)

2: If Q1 is "dead" , does anyone know a replacement from the marking & symbol ???

Any hints are most welcome

/Bingo

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Hmmmmm

According to this http://www.tkb-4u.com/code/smdco...

The 1AM could be a Motorola 2N3904
1AM MMBT3904L Mot N SOT23 2N3904

I have some BC850-C could i use those as replacements ??

/Bingo

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No, the output isn't RS232. No doubt there's a control box to go with this pen that contains a micro. The pen puts out raw barcode pulses and the micro in the control box reads and interprets them, calculates the barcode value and streams it out in ASCII, either RS232 or in pretend-keyboard format.

The center pin of the SOT23 is the collector, if it's a transistor. You may need a pullup resistor from the red wire to the orange. Try a 10k resistor and see what happens.

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Dammmm :evil: :evil:

It seems that all i needed was a pullup on the data line :evil: :evil:

I have put 10K from VCC to the dataline , and now the 3904 is "Pulling" low as it sees signal , anyone knows if 10K is a reasonable value ?????.

Now i just need to adjust the sensitivity , as i did turn the "base pot" in desparation :oops: :oops:

/Bingo

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10k should be fine.

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Bingo600 wrote:
Dammmm :evil: :evil:

It seems that all i needed was a pullup on the data line :evil: :evil:

I have put 10K from VCC to the dataline , and now the 3904 is "Pulling" low as it sees signal , anyone knows if 10K is a reasonable value ?????.

Now i just need to adjust the sensitivity , as i did turn the "base pot" in desparation :oops: :oops:

/Bingo

@Peret

Ohh i actually did not see your post , before i posted the above.
But we both came to the same conclution :-) ... me by fumbling around. And listening to the little ringing bell that says this circuit can pull something to ground ... And i could not see any pullup resistors on the Red (data) line , so i tried the 10K.

And my above statement is not correct , it seems that the 3904 is always pulling low (active) , and then "releases" when it sees a pulse from the light sensor.

Thank you guyzz , i love being on this forum :-)

Its not easy to see any "pattern" on my 50Mhz Analog Hameg Scope, except that it "pulses"

But i now get something that could resemble a "barcode" on my LS-Analyzer , when i do a swipe.

Allthough it needs a lot of "cleanup" in software....

Time to go to the Academy and get Dave Van Horn's project , and his homepage also have a nice tutorial.

/Bingo

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Only some thought. I had found that with this BJT perhaps you need an small resistor (perhaps about 1K) if you have frequencies above 1MHz, because turn it off is slower than turn it on. Thats because the small capacity stores enough minority carriers that should be removed, and the only one that does this is the resistor. So the smaller the resistor, the highest the current that discharges the parasitic capacitor.

Barcode readins is achieved comparing the 'short' and 'long' pulses to find the sequence ,ie short-short-short-long space could mean 8 in the EAN-128 barcode. Interpretation of this sequence depends on the standard of the barcode.

Guillem.

Guillem.
"Common sense is the least common of the senses" Anonymous.