Introduction: Reverse Engineering

Many of the members here at Instructables ask about datasheets or pin outs of a device or display in answers, unfortunately you cant always get a datasheet and schematics, in these cases you only have one choice reverse engineering.

Reverse engineering is a skill that is not taught in college or university electronics courses and yet it is a valuable tool in an engineer’s tool belt. Many people working on electronic equipment search to no end for schematics for a device when if they knew how it in all probability it would take less time to make their own schematics and parts lists.

Take the flash circuit in this Polaroid Camera, if you wanted to model a capacitor charger after the flash circuit in this camera, unless you worked for Polaroid your chances of getting a schematic are next to impossible. Other than the resin covered custom IC the rest of the circuit was easy to trace and make a schematic of taking me just four hours.

You can hand draw your schematics, build them in paint like I do, or build your schematics a circuit simulator like 123D Circuits where they are easy to read and you can test them making sure you made the schematic correctly.

I am going to show you some of the things you need to know to reverse engineer.

Step 1: Reverse Engineering Surface Mount Device (SMD) Circuit Boards

Although through hole circuit boards and SMD circuit boards look quite different they work the same way and they are reverse engineered the same way. Through hole components are the first components engineers learn to read, however surface mount devices, (SMDs) are not as easy to read because of the small aria for a part number or color codes. To identify components correctly you need SMD code books and SMD codes I have attched these in PDF format.

SMD resistors codes are alphanumerical however they are not that different than resistor color codes, the first number is the first digit, the second number is the second digit, the third number is the multiplier, and the R is the decimal place. So 103 is 10 kΩ and 4R7 is 4.7 Ω almost like the code on ceramic capacitors only with capacitors the letter is the tolerance.

SMD ICs have more information on them like 74HC595 or HC595. The through hole device is SN74HC595 and most of the time the datasheet for the through hole will do the same thing however not all the time. To get the exact datasheet for most SMD ICs use the part number prefix MM, so SN74HC595 is MM74HC595 and you can get the datasheets at these web sites.

http://www.maxim4u.com/

http://www.alldatasheet.com/

For SMD transistors and other semiconductors you need code books like the ones in PDF format here, on the semiconductor you will see a code like 2X F. When you look up the code in the code book it gives you the SMD part number MMBT4401 and the through hole part number 2N4401.

Step 2: The Schematic of the SMD Circuit Board

Now that you have the values and datasheets for your components you can make a schematic of the circuit board. For this part sometimes I remove the components, photograph the circuit board, and trace out the conductors in paint. Start at one pin and follow the conductor to the first component draw the pin and wire and the component if the conductor branches off draw it to the next component. Once you have drawn all the branches of that conductor go to the other side of the first component and draw the next conductor and its branches to the components it goes to. Continue this until you have drawn the schematic of the circuit board.

Parts
Three capacitors 10 nf
Two-4 bar 103 is two-4 x 10 kΩ resistors
Two-4 bar 75R0 is two-4 x 75 Ω resistors
Two x 392 is 3.9 kΩ resistors
Two x 51R1 to 2 LEDs is two 51.1 Ω resistors
Three x 82R5 to 3 LEDs is three 82.5 Ω resistors
Four x 68R1 to 4 LEDs is four 68.1 Ω resistors
One x 42A04F8, HC163 is MM74HC163 or SN74HC163 IC
Two x 42A74HT, HC595 is MM74HC595 or SN74HC595 IC
Two x 2X F is MMBT4401, SO4401, or 2N4401 transistors
Kingbright SA43-21GW  SA43-13GW one digit 7 segment LED display

Step 3: Reverse Engineering a Component

Sometimes you need to reverse engineer a component because you can’t find a datasheet for the component. This is common with components that don’t have part numbers on them like Chip on Glass Liquid Crystal Displays (COG LCDs) and Light Emitting Diode (LED) displays.

Many people salvage parts from used electronics like the display in this alarm clock and when they go to use it in a project they can’t find a datasheet for the display. All you can tell is it is a four digit seven segment display and they spend hours trying to use a meter to find the pin outs. Before removing a component from a circuit board find the datasheet for the component or reverse engineer the pin outs.

Weather a COG LCD or a LED display they are reverse engineered the same way, follow the conductors from the display to the driver IC and look up the IC.

Step 4: Cleaning the Circuit Board

Quite often the circuit boards are dirty with debris and scuffs on the components making the circuit board and components unreadable. To clean them I use a rag, a paintbrush, and methanol or rubbing alcohol, to clean the parts. This makes the components part numbers and color codes more readable and it is easier to see where the conductors go.

Do not smoke or clean the circuit board near an open flame, alcohol burns.

Do not rub to hard or printed on part numbers can be removed.

Step 5: Start Engineering

Now that you can read the part numbers, color codes, and conductors, it is time to start reverse engineering the component you cannot get a datasheet for.

Start by following the conductors from the component you cannot get a datasheet for to its driver, in this case a LM8560 IC.

Look up the IC and get the datasheet, you can do this by looking up the LM8560 in a data book or by looking it up at these two web sites.

http://www.maxim4u.com/

http://www.alldatasheet.com/

Once you have the datasheets find the pin outs and start tracing out the conductors.

Step 6: Tracing the Circuit

Like I did in the SMD circuit board I photographed the circuit board and traced the conductor’s one or two at a time and drew the conductors and components in a partial schematic since I only wanted to make a datasheet for the LED display.

I repeated this process until I had all the pin outs of the LED display.

Step 7: The Final Pin Out

After I made partial schematic of the LED display and its connections to the IC and the rest of the circuit board I checked the circuits in the display with a meter and made a schematic of the display. Now when I go to use the LED display in a project I already have the pin outs.

Step 8: 4 Digit 7 Segment Display With Decimal Point

Some 7 segment LED displays are hard to get datasheets for and common anode and common cathode cannot be determined by just looking at the display. But when you look at the circuit board the transistors indicate which pin is the common cathode or the common anode by going from the pin to ground or Vcc. The SN74HC595 IC makes it a simple matter to decipher the LEDs segments a, b, c, d, e, f, g, & DP. 

With the SN74HC595 QA connects to segment a, QB connects to segment b, and so on until you get to QG to segment g. QH connects to decimal point, and QH’ connects to the second SN74HC595 to drive the anodes of the individual digits.

This LED display is a serial input parallel to the common anode 4 digit 7 segment LED display with decimal point. Now I can make my own datasheet for the Common Anode 4 Digit 7 Segment LED Display.

Step 9: Mystery Circuits

I look for things to do so I salvage, on one of my salvaging forays I came across this circuit. At first I thought it was an audio amplifier for a PC but when I looked at it more closely it only had power in and 4 outputs, no audio input. It had to be some kind of adjustable power supply, so I reverse engineered it.

Step 10: Mystery Circuit Schematic

As I explained in the earlier steps of this Instructable I started by looking up the components and making a parts list. Once I had a parts list I started at one pin and traced the conductors to the components and from the components to the outputs. As I traced the conductors I made the schematic.

Step 11: Adjustable PC Power Supply

Once I made the schematic and the parts list I built the circuit in a circuit simulator. Faster than doing the math a circuit simulator can give me test points and values I can use in the real world to determine if the circuit is working as designed.

This circuit is a 160 watt adjustable power supply for inserting into a PC beyond that I can only guess at its purpose, it is ether a supply for specialized accessories or converting a tower to a complete electronics lab with adjustable power supply.

Reverse engineering circuits and components gets you schematics for electronics you cant find schematics for and tells you pin outs for components you cant find datasheets for, a useful tool in your tool belt.

Comments

author
EToft made it! (author)2016-09-02

Is there any way to determine the capacitance of one of those tiny...head of a pin tiny...capacitors. they have no markings that I can make out.

author
Josehf Murchison made it! (author)Josehf Murchison2016-09-02

Yes; but it is not easy, you need a capacitance meter that will measure 1 pF. Then you may need to solder a lead on them and test them with a capacitance meter, however it wont work with just any multi meter that measures capacitance I have a Fluke meter that wont measure under 100 nF a Gold that wont measure under 100 pF and a Smart bench meter that measures down to 1 pF but it's not cheep. A good meter like this one can cost you a grand, it tests transistors capacitors frequencies even decibles and hFE of transistors

IMG_8976.JPG
author
ArifSae made it! (author)2016-03-26

Hi, A request, since everyone has smart phone and especially dead smart phones :P It would be a great help if you can make an instructable on using smartphone screens. I have such a screen from old phone and its a pain to see it wasted. I was unable to find any pinouts after days of searching

480x800 - 4inch lcd
LCD number: BLU4003-20
for mobile: FLY iQ445 Genius

27 pins

author
Josehf Murchison made it! (author)Josehf Murchison2016-03-26

Not everyone has smart phones. I'm blind and I can't see a screen under 19 inches.

But you can find the pin outs for yourself just follow

https://www.instructables.com/id/Live-Reverse-Engin...

and my other Instructables on reverse engineering.

author
Archit B made it! (author)2016-03-21

I have a working at&t tochscreen phone eith a 1.3 mp camera and an arduino uno R3 board.How can i make a cctv camera using these as my budget is much low cause its my first time so PLEASE HELP !!!

author
Josehf Murchison made it! (author)Josehf Murchison2016-03-22

Since it is a working phone follow this Instructable to get the pinouts of the camera and the screen,

https://www.instructables.com/id/Live-Reverse-Engin...

Keep the ribbon connectors like this Instructable,

https://www.instructables.com/id/Salvaging-Liquid-C...

Then there are a number of Arduino Instructables like this one,

https://www.instructables.com/id/Arduino-Ethernet-C...

author
Javastar18 made it! (author)2015-10-21

I have a dead Nokia lumia, any advice to try and get the camera to output a composite signal?

author
Josehf Murchison made it! (author)Josehf Murchison2015-10-21

Is it totally dead, or can you charge the battery and bring up an image through the camera?

Depending on the camera it can have 4 to 30 pins.

4 pins is easy.

pin 1 Vcc

pin 2 clock

pin 3 data out

pin 4 ground

If you can bring up an image through the camera and you have a multi meter and an oscilloscope you can try what I did in this Instructable.

https://www.instructables.com/id/Live-Reverse-Engin...

author
cobourgdave made it! (author)2014-03-02

Nice job. Excellent suggestion using the paint, I become very confused tracing leads on a tight board.

author
Josehf Murchison made it! (author)Josehf Murchison2014-03-02

It takes a nice clear pic and it works well.

I am visually Impaired and just to see a circuit board I need a magnifying glass, on my computer I can blow up the pic and trace the conductors with ease.

When I trace a conductor I save as so I don't loose the original pic.

author
LegendofPedro made it! (author)LegendofPedro2015-08-16

Have you tried using a scanner? I pefer it as clear pictures are easier to obtain.

author
Josehf Murchison made it! (author)Josehf Murchison2015-08-16

I also prefer the clear picture of a scanner I have a 4 input Tektronics oscilloscope but logic circuits are to irregular to make sense of the images to read the binary so I use a home made capture circuit.

author
kschmidt2 made it! (author)kschmidt22014-04-14

something you can do if you're comfortable dissasembling your ipod, take it apart till you get to the camera, then screw the lense all the way in. It magnifies so much that you can see the Clusters of Red, green and blue pixels in an LCD screen. otherwise, pull apart a digital camera and get the zoom drum out. Perfect for it.

author
Josehf Murchison made it! (author)Josehf Murchison2014-04-14

My wife won’t let me play with the Ipod in fact every time I get something she checks it out first and if she wants it I can’t play with it.

We got our first Ipod when I was driving truck, I stopped at a truck stop to use the john and coke was having a contest and I happen to pick up a bottle cap off the ground and it said win a free Ipod. Later she traded that one in when she got a new one that had the screen and camara.

The digital cameras I get are usually busted up but some of the phones I get have the neatest cameras with as little as 4 conductors +V –V clock and serial data out.

author
kschmidt2 made it! (author)kschmidt22014-04-16

Haha, that figures, since the iphone 5 came out, you can generally get ipod and iphone 4's of ebay pretty cheap, so just grab one of them and you have an electric magnifying glass. And what I meant with the digital camera drum was to just use the drum like a magnifying glass, they do the same magnification.

author
Josehf Murchison made it! (author)Josehf Murchison2014-04-16

I will have to check that out, right now I use a microfilm projector lens to read circuits.

author
GallegoPunkrocker made it! (author)2015-06-19

hey man! i already finish to read the complete article! that's so good! thank you for your sharing! i'm electronic tecnician and that way of thinking just give me a great solution for a circuit unknown for me!

PD:srry about level of english

thanks from argentina

author
Josehf Murchison made it! (author)Josehf Murchison2015-06-19

Your welcome

author
mnp161 made it! (author)2014-12-29

This is by far the best and most useful guide I have ever came across. I graduated with an E.E. degree, and we never reverse engineered any type of electronic device... go figure.

author
Josehf Murchison made it! (author)Josehf Murchison2014-12-30

Back when I started in electronics there were no computers, internet, or calculators, everything was vacuum tubes and they were just starting semiconductors, most of them were crystals. So when we came across something we never saw before it was make your own schematic, because it was almost impossible to get one.

I’ll tell you a trick we had for calculating resistors in parallel of different values in our head, the answer is in significant digits the way it should be.

First take resistors over 20 ohms or more larger than the smallest and ignore them, make sure they are all Ω, KΩ, or MΩ.

Second take the smallest resistor and subtract it from the largest resistor.

Take that number and divide it by two if you have an even number of resistors or divide it by three if you have an odd number of resistors.

Add that to the smallest resistor and divide by the number of resistors and you have the RT.

8Ω + 10Ω + 12Ω + 16Ω = 16 – 8 = 8/2 = 4 + 8 = 12 / 4 = 3Ω RT

It works the same way for capacitors in series.

Joe

author
Cheerfultrout made it! (author)2014-07-29

nice instructable, hadn't thought of using paint, much simpler than what I do which is use the nubs on the bottom of boards to pierce holes in a piece of paper and then I basically recreate the board on paper and use light shining through the back to see both sides at once and work from there. Using paint seems like a much easier solution, definitely going to use it next time.

author
Josehf Murchison made it! (author)Josehf Murchison2014-07-29

Just a hint I forgot to mention in the instructable.

Photograph the assembled circuit that way if you need to remove a component to see the conductors under the component you have a visual record.

Joe

author
goldenshuttle made it! (author)2014-03-27

This is one of the best Instructables to date. Supplementary codes are very valuable too...Many thanks ...

Did you try hacking a Camera with face detection ? connect to a servo to follow the face ? did you hack if inside the camera face detector is a seperate chip or built in the sensor chip ?

author
Josehf Murchison made it! (author)Josehf Murchison2014-03-27

Thanks.

I haven't done a camera with facial recognition yet but I have done all kinds of TV's, camera flashes, solar lights, displays, and scanner printers.

This is something I learned before the WWW.

Joe

author
SuperTech-IT made it! (author)2014-03-06

Thanks. It's nice to have all these documents in one place.

This will probably save a lot of people a lot of head scratching and frustration!

Kudos.

author
Josehf Murchison made it! (author)Josehf Murchison2014-03-07

I am glad you like it.

I thought it best to include the datasheet links and code books to save my readers from searching for them, they are not that easy to find If you don’t know what to Google.

A lot of people are scratching their heads on pin outs for things they can’t get datasheets and schematics for.

This Instructable was needed and it is something I do all the time.

author
dkirkland3 made it! (author)dkirkland32014-03-22

Hi I'm new to the site and I have no idea how to use it. I have some questions about your gold extraction methods. Can you please email me
daniel.kirkland92@gmail.com

author
SuperTech-IT made it! (author)SuperTech-IT2014-03-22

You are going to want to put this as a reply to the author of the instructable you are referring to, or at least within the instructable you are inquiring about. You sent this message as a reply to something I had said in a completely different instructable, and as such, myself and the author of THIS instructable were likely the only ones alerted to your inquiry. Personally myself, I have no knowledge of the instructable you are referring to. Sorry.

author
dkirkland3 made it! (author)dkirkland32014-03-22

Is there any way to direct message? Cuz I think he is the same guy who posted this instructable cuz I saw his name in comments. It was just a newer instructable and I figured he would have a better chance at seeing it.

author
SuperTech-IT made it! (author)SuperTech-IT2014-03-22

Ya, what Josehf Murchison said! LOL!

author
Josehf Murchison made it! (author)Josehf Murchison2014-03-22

That is OK I got the message.

Here is the first thing you should learn never post your Email it opens you to junk mail and all other spam.

Click on the authors name in orange and it sends you to his home page where you can click on Private Message and only he reads it.

Joe

author
SuperTech-IT made it! (author)SuperTech-IT2014-03-07

It will certainly come in handy when repairing Macbook motherboards.
I hate seeing some 3 legged device marked "K72" or something like that and wondering what the heck it is exactly.
For the most part, you can find Macbook mainboard schematics, which makes it a lot easier, but sometimes it's a lot easier to just be able to know what part you are looking at.

author
billbillt made it! (author)2014-02-28

great

author
Josehf Murchison made it! (author)Josehf Murchison2014-03-03

Thanks

author
thegoom made it! (author)2014-02-27

This is a computer fan speed controller.

author
Josehf Murchison made it! (author)Josehf Murchison2014-02-27

In other words a quad adjustable power supply.

author
thegoom made it! (author)thegoom2014-02-27

Or a quad array of potentiometers.

author
Josehf Murchison made it! (author)Josehf Murchison2014-02-27

If you look at the schematics, the pots control the TIP31A transistors the transistors regulate the power out of the circuit.

The quad op amp turns on the LED when that channel is in use.

What this Instructable is about is schematics and pin outs of components when you cant get them,

author
socalcovey made it! (author)2014-02-27

thank you for putting in the time to explain this topic. I enjoy tinkering and with this info I can really take it to the next level.

author
Josehf Murchison made it! (author)Josehf Murchison2014-02-27

Your welcome.

author
discostu956 made it! (author)2014-02-23

Nice and helpful, well for electronic gumbies like me. Thanks for putting this up

author
Josehf Murchison made it! (author)Josehf Murchison2014-02-23

Your welcome

author
petrucci made it! (author)2014-02-23

Sometimes it's helpful to hold a pcb against a bright lamp to trace it.

author
Josehf Murchison made it! (author)Josehf Murchison2014-02-23

It helps when you can see through the pcb and it is printed on both sides.

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Bio: I am a photographer, a tinker, an electronics technology engineer, and author; I write short stories and poetry for the love of writing. I started ... More »
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