Pocket 256 Bit Logic Analyzer




About: 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 writing poetry in high school over thirty years ago where I ...

This is a pocket size 256 Bit eight input digital analyzer for checking digital circuit functions that I built for my own use at home. It cost less than twenty dollars to build and it enables me to test switching circuit functions at slow clock speeds as well as I can check 256 bit counter outputs. This analyzer works well and is cheap to build.

Step 1: 555 Timer

If the clock on your circuit is too fast you won’t be able to see the functions. To aid with testing on prototypes I built this variable speed 555 timer clock so I could adjust the speed of the flashing LEDs while checking circuit functions.
  1. 1 555 timer
  2. 1 LED
  3. 1 2N3904 transistor
  4. 1 switch
  5. 1 50 k& pot
  6. 2 1 k& ¼ watt resistors
  7. 1 150 & resistor
  8. 1 33 uF 6 Volt capacitor
  9. 1 47 uF 6 Volt capacitor
  10. 1 proto board
  11. 1 8 pin IC socket
  12. 1 pot knob
  13. 4 feet or mounting posts
  14. Wire

Step 2: Operating the Analyzer

This analyzer works very simply, when hooked up to 5 volts power the green LEDs light up indicating high or the binary 1.

When the inputs are connected to a circuit or ground the green LEDs turn off and the red LEDs light up indicating low or the binary 0.

As the circuit the analyzer is conected to runs the LEDs switch from red to green indicating 0 or 1 on the input as shown on input #1 here in image #3.

Step 3: The Analyzer Circuit

Each input is very simple on its own consisting of:
  1. 1 red LED
  2. 1 green LED
  3. 2 150 & ¼ watt
  4. 2 18 k& ¼ watt
  5. 2 2N3906 transistors
  6. 1 inverter

However 8 inputs multiply the circuit 8 times that is:
  1. 8 red LED
  2. 8 green LED
  3. 16 150 & ¼ watt
  4. 16 18 k& ¼ watt
  5. 16 2N3906 transistors
  6. 2 DM74LS04 hex inverters
  7. 2 14 pin IC sockets
  8. 1 proto board
  9. 4 feet or mounting posts
  10. 1 10 pin connector I used a 14 pin IC socket
  11. Wire

I looks more complcated then it is.

Step 4: The Analyzer in Operation

Once you build the analyzer you can start testing circuits.

Since I did not ground the last three inputs this circuit should put out a digital output on the green LEDs of:


and back to 00100111

Watch the green lights in the video
Make It Glow

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    34 Discussions


    6 years ago on Introduction

    Great Project, a link went to my Gizmo blog:

    2 replies

    Hello, nice project! I did something very similar to help me test digital circuits.


    I think the main difference is that mine only lights up the green LEDs on a definite logic HI signal instead of always being lit with the absence of a logic LOW signal as yours does. It has 12 indicator bits because I use two 7404 chips (6 x NOT gates) to do the signal level checking, hence, 12 outputs. I also threw on a row of dip switches for testing digital inputs. Lastly, I found it useful to be able to supply various voltage levels, so an on board 5V regulator is available, but can be bypassed to allow direct sourcing of 5V or 3.3V. 

    I am also a bit confused about the clock... I understand it's importance if you were buffering the indicator outputs so you could literally slow down the output signal (until the buffer was full). In that case, the clock could control the buffer output speed, but that doesn't seem to be the case.

    On second look, it appears you are you using the clock to control the digital input of the circuit being tested. Is that the case?

    Regardless, nice work!

    2 replies

    Yours looks nice
    It looks like you hot glue your components in place before you solder them.
    Funny how you can do the same thing different ways.
    How is yours for loading effects on the test circuit?
    The timer is for testing circuits with external clocks or clocks you can pull.
    The red LED indicates full transition from one state to the other without the red LED you can have partial transition and no indication of it.
    To me it also makes it easier to see negative or positive transition functions.
    For instance in the modified sine wave signal generator circuit I was testing in the video, the toggling JK flip flop must toggle during negative transition of the timer signal or the And gates can trigger for a couple Nano seconds when they are not suppose to.

    Thanks, and that makes sense for the clock. And yes, I hot glued a few things down, but only after I had finished it... I tend to break things off sometimes, especially the dip switches - after pushing the switches back and forth for so many times, the solder joints start to get weak. I haven't noticed any load effects at all. At most, the test circuit line(s) would have to sink/source about 5mA for an LED to turn on. I guess I haven't really worried about unexpected transitions since I don't use this circuit for anything very fast. If I can't see the transition from red to green, then this thing wouldn't be any help in testing the circuit. I have a USB logic analyzer for that! Again, nice 'ible.


    6 years ago on Introduction

    Thanks very much for a Great able ,I have made one & it has really helped out,my question is , how is the 555 clock hooked up to buffer a circuit that is to fast to see?have made the clock unit ,have not been successful using it to slow the circuit down..Thanks very much for your help.

    1 reply

    I use the clock two ways.

    The first way is when I can bypass the circuits own clock. Some circuits you can disconnect a wire or pull an IC.

    The second way is like a strobe, with a strobe light you can make a fan blade look like it is standing still or turning slowly. You can do the same with the signals by adding and gates on a bread board.


    6 years ago on Introduction

    Any device that helps is good and it is such. Is useful for constructing simple logic. With this device you can not say that is the 256 bit but 8 bit. I called them, 8 channel Analyzer logical States. On 8 bits, you can view the maximum number of decimal 256. You can also upgrade by adding more modules, thereby creating a 256 bit or channel Analyzer. Maybe the author had in mind.

    2 replies

    I only called it a 256 because if you connected it to a counter it would show a 256 count and I mixed up my bits and bytes I just crossed my kibbles and bits.

    It works good at showing the embedded programing of a circuit.


    Josehf Murchison

    Reply 6 years ago on Introduction

    Yes and more.

    There are two reason for the red LEDs first they indicate complete transition from 1 to 0 in the embedded programing.

    Second they make the edge triggering, negative and positive transition of a function easier to see and explain.

    Starting from the left, if you watch LED 1, 2, and 3 in the video, LEDs 2 and 3 toggles only when LED 1 goes from green to red.
    Negative transition

    LEDs 4 and 5 only go from red to green only when LED 1 goes from red to green.
    Positive transition

    So LED 4 only comes on when LED 2 is on, and LED 1 turns on, and LED 5 only comes on when LED 3 is on, and LED 1 turns on.

    I should say embedded programing is fixed programing in the circuit and it is not reprogrammable like software, so you have got to get it right when you build the circuit, or you rebuild the circuit.



    6 years ago on Introduction

    Bearded RTL DTL TTL Guys Rule The 1974 74's and we are practical people who don't spend our lives trying to prove how smart we are :) When I started LS TTL was new.

    1 reply

    When I started in electronics everything was vacume tubs solid state was US milatary, there was no such a thing as a pocket calculator you did math long hand or in your head I would like to see these young bucks try that.


    That is what it is ment to do. When you build a circuit like the Modifide sign wave signal generator there are very spsfic internal high/low signals you need to make the circuit work the way you want. This circuit tells you if you are geting those high/low signals.


    it is only 8 bit (or more properly 8 channels, 1 bit), not 256. I'm still not sure why a clock is needed though.


    Each green LED is a bit and 8 bits is a byte making a numerical max of 256 in binary language. If you were to add one green LED it would be a 512 add another 1024 and so on. However that would be a byte and two bits.
    Can not resist the joke here but nobody would give two bits.
    The external clock is only needed if you can not manipulate the internal one all binary circuits have a clock of some kind.