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Lord Banshee
Joined: 18 Feb 2007
Posts: 24
Location: USA
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 09 Jul 2007 18:50 a7w diode |
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Ok well am trying to figure out how a little electronic device works but sort-of reverse engineering how it is connected but i have run into problem with little IC's that i can't find info on maybe you guys can help me out.
There are 3, three-pin IC's i think it is a SOT-23 package. At first i thought it was some kind of vreg but it doesn't seem to be the case in terms of measuring the voltage as all the pins.
The three IC has the following codes on them, 5CW 5n, A7W 5n, and WJ(s with an arrow under it) 5? where the ? is something i can not make out so i guess it is an "n" also, so the last one is WJs 5n i think. my guess is the 5n is 5 nanosec so maybe these are logic device??
These little chips are connected or around the power source with a couple of resistors and capacitors. I can take a pic and upload it if it helps.
Any hep you can give me will be greatly appreciative, thanks.
-Chris
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Eugen_E
Joined: 29 Nov 2004
Posts: 358
Helped: 31
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09 Jul 2007 21:53 a7w transistor |
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I think they are just transistors.
With resistors and capacitors they can form a kind of oscillator to drive a piezo buzzer, speaker, LEDs...
It would be very helpful to tell us what is the purpose of this circuit, and what are the other devices around it. Also the picture would give more details.
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Lord Banshee
Joined: 18 Feb 2007
Posts: 24
Location: USA
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09 Jul 2007 22:43 5cw smd |
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yes a transistor would make sense there i think 
i have idea what the circuit is doing but it does have a neat turn on feature that i am not sure how it is doing it, yet.  There is 4 buttons, when off the only thing getting power (9V batt) is a couple of these ICs and that it. When you push the on button the power is transfer to the rest of the componets such as 4v reg and a 3.3reg to power the MCU and LCD. Here is a pic of the device side.
On the pic, when the on button is pushed ON_B is shorted with ON_A, giving ON_A the voltage at B which is ~8.8V. As you can see these 3 pin devices are in the bottom left.
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echo47
Joined: 07 Apr 2002
Posts: 4206
Helped: 566
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Lord Banshee
Joined: 18 Feb 2007
Posts: 24
Location: USA
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12 Jul 2007 17:11 5cw transistor |
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Thanks guys still trying to figure it out, haven't spent too much time on that part of the circuit. But i did open up another one of these devices and i can still all the number on all of them now. The correct numbers are:
5CW 59
A7W 59
WJ^s 57
so the 5n turned into a 59 and 57.
Also i took some quick voltages when the device is on and then the device is off
So the device is a SOT23 package and the pinout is the following
1--| |
* *| |--3
2--| |
Off, connected to 9V batt
5CW (1)=9.0V (2)=9.59V (3)=0.0V
A7W (1)=9.0V (2)=9.21V (3)=9.48V
WJs (1) =0.0V (2)=GND (3)=9.48V, pin1 is connected to cathode side of a LED
On
5CW (1)=8.54V (2)=9.3V (3)=9.26V
A7W (1)=8.54V (2)=7.62V (3)=7.88V
WJs (1) =1.5V (2)=GND (3)=0V
Pin3 of the 5CW is the pin going to the regulators for the MCU thus the main power. Just got to figure out exactly whats going on to make this happen.
Thanks Again
Added after 2 hours 21 minutes:
OK i figure out this circuit with the help of SPICE to confirm.
The WJs transistor is turned on when the MCU outputs 3.3V in turn causes a voltage drop across the resistor between A7W(3) and WJs(1) do to the new following current. This gives raise to the voltage drop of a diode between A7W(3) and A7W(1) which connects to 5CW(1). Which allows enough voltage of V_BE for that transistor to turn on which then opens up 5CW(3) to 5CW(2) allowing current/voltage from the battery to power the circuits.... So i think
Now the problem i have still is how is the MCU sending out a 3.3V before it gets power lol. From what it looks like is 9V that goes into the inverter input LCX14 when the main button is pushed and "MAYBE" it can turn on the LCX14 without it have VCC and somehow it transfers that VCC long enough to the MCU which might have a automatic pullup-resistor output to 3.3V. And it is long enough to turn on the WJs transistor giving raise to the first paragraph which powers the vregs.
Just a good guess or is this how it might work?
I've include pics of spice with those transistor laid out like the above PCB picture.
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12 Jul 2007 17:11 Ads |
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CAVERMAN
Joined: 19 Jul 2009
Posts: 2
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19 Jul 2009 1:49 transistor a7w |
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| Interesting set of posts. I too am lookin at this module and did not realise the LED was a LED as I had never looked at that side of the board when powered on.
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