Introduction: Pocket 256 Bit Logic Analyzer

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.
Parts
  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:

00100111
10101111
01000111
11010111

and back to 00100111

Watch the green lights in the video

Comments

author
Edgar (author)2012-11-15

Great Project, a link went to my Gizmo blog:
http://faz-voce-mesmo.blogspot.pt/2012/11/instructables-sofa-de-paletes-stereo.html

author
Josehf Murchison (author)Edgar2012-11-15

Dude that is a cool page thanks.

author
Edgar (author)Josehf Murchison2012-11-15

Thank you, I try to promote empowering stuff.

author
Kurt E. Clothier (author)2012-11-13

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

http://www.projectsbykec.com/projects/electronics/digital-design-helper

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!

Modified.jpg
author

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.

author

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.

author
Hanni43 (author)2013-04-17

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.

author
Josehf Murchison (author)Hanni432013-04-17

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.

author
jensenr30 (author)2012-11-25

Great project!
Is there any reason to have the two sets of eight LEDs (the red and green sets)?
Is it to make sure your device is always correct in case one LED doesn't turn on as it is supposed to?

I would very much appreciate an answer. Thanks!

author

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.

Joe

author

cool. and thanks!

author
naplatki (author)2012-11-18

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.

author

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.

Joe

author
petrovias (author)2012-11-16

Why do people not use their real names when they want to preach to you :).

author

Google Amanda Todd

author
petrovias (author)2012-11-16

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.

author

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.

author
mettaurlover (author)2012-11-12

Useful, yes. Terrifyingly confusing, also yes.

author
quatch (author)mettaurlover2012-11-12

I can't quite figure out what it does beyond show high/low for 8 channels.

author
Josehf Murchison (author)quatch2012-11-12

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.

author
quatch (author)Josehf Murchison2012-11-12

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.

author
Josehf Murchison (author)quatch2012-11-13

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.

author

8bit = 256 values. 256bit = 1.157920892373 × 10^77 values

author

Actually he is right, this is only an 8 bit LA. You're confusing terminology. 8 bit allows you to have 256 different values but that doesn't mean it's 256 bit.

Either way, the terminology is still wrong. We use the term channels for a logic analyser to avoid confusion when configuring the device. Most professional logic analysers have features to analyse 8, 16, 32, 64 and 128 bit busses, but they need a respective number of channels to do so. So you need to assign channels to measure said bus. But I'm getting off-topic here.

Strictly speaking there is a better way to look at fast signals in a simple reliable way. You need to use a long shift register per channel. Read in bits at the system clock speed and then replay them slower. It's a bit trickier but it's still fairly fast and more than sufficient for most amateur applications. Though that won't help you detect glitches.

A warning: For debugging more substantial logic circuits using a 555 timer to slow down the system clock isn't a good method. Half the problems only occur when speeding up a circuit. Flip-flops can become unstable, line impedance starts becoming noticeable above 10 MHz. Now this isn't a problem with most modern microcontrollers as they have very good output buffers that can simply pull the line to the right level as long as you keep the fan-out limited. Capacitive coupling also only occurs at the higher frequencies. So be careful when trying to look at a design like this. Some logic also requires a minimal frequency to work properly!

Another problem I notice with your circuit is that you drive the transistors way into saturation. Considering the speeds you're working at that isn't a problem. But if you ever try to use transistors at higher frequencies do keep that in mind.

Also maybe this can give you some good ideas; Ai Lee Kuan wrote a great article on the basic operation of a logic analyser: http://www.eetimes.com/design/programmable-logic/4015108/A-How-To-tutorial-on-logic-analyzer-basics-for-digital-design

author

$10.00 is a lot less than $21,200.00 for a TLA6404 Logic Analyzer.

256 bit color graphic programing.

In truth it is 256 byte as it displays 256 different bytes I just crossed my kibbles and bits.

I could hook up my 7 Oscilloscopes to a circuit I have 3 EICOs, 2 Sencores, 1 a dual trace oscilloscope, and a DSO Nano digital pocket oscilloscope, DSO 062 Oscilloscope, just looking back and forth from seven screens is hard on my neck and the analog scopes look funny when hooked to digital circuits.

You got to admit $10 verses $21,200 OK I didn’t pick the cheapest analyzer ether.

author

I don't think you quite got my point. I'm not saying you should buy the expensive Agilent/HP, Tektronix, R&S, LeCroy, ... equipment. Do use it if you have access to it! A good LA can save you a few days debugging a circuit! I'm just saying that those devices have quite a few extra features and that the documentation might give you some good ideas for future versions of your circuit.

A small $30 FPGA development board plus a laptop will do a pretty good job. A cheap microcontroller will work quite well if you're working on something with a low frequency. There are several examples of both on the internet for people who are interested in those things.

I'm not quite sure why you're going on about the byte thing at this point as LAs are simply specified with channels just like scopes, network analysers, spectrum analysers, communication analysers and other such devices. 

Using a scope is a bad solution for this actually. Logic analysers and oscilloscopes have a very different goal, they also load the circuit differently. A scope will always have its 1MOhm and 15-25 pF input assuming you use normal probes. For higher frequencies this becomes the standard 50 Ohm port. Combined with a regular 1:1 or 1:10 probe. While logic analysers typically have an input impedance in the range of 20kOhm, the capacity is even more complicated as it depends on the type of probe used. It ranges from 5 pF for old fashioned clip on probes to 0.5 pF for the connectorless probes. Additionally it comes with buffer circuitry but that's very manufacturer dependant. A logic analyser is designed to have minimal influence on the way the logic circuit behaves compared to a scope. Using multiple scopes might be tricky as you'll have to share the triggering between all of them. Sounds like a coax and BNC T-piece nightmare in the making!

An additional thing is the level detection. An LA will see the signal as digital components do. It'll also detect transitions, glitches, etc... All of this can be detected automatically, where using a scope might make you miss such things. In fact, if it's a low bandwidth scope it might not even be able to see very sharp spikes as digital logic is blazing fast compared to cheaper DSOs. The old analog memory scopes might perform better at this as they'll likely show a smudge (very interesting to experiment with those scopes for such things). And using a regular analog scope for digital logic is a joke. Actually, on to the subject of scopes again, even more interesting are the mixed mode scopes, I just love the Agilent scopes with the 16 channel LA pods. Saves you so much trouble when dealing with Analog-Digital conversion!

author

Can you say Ha Ha Ha

author

You are correct in saying that each green LED is a bit and that therefore it is an 8 bit system but it is definitely not 265 bit as that would require 256 inputs, and that would be a lot of wire! It is also true that an 8 bit system has 256 different states eg 00000000 to 11111111 but as quatch says it is only an 8 bit system. Nice instructable though.

author

256 bit color graphic programing.

In truth it is 256 byte as it displays 256 different bytes I just crossed my kibbles and bits.

author
mlah (author)Josehf Murchison2012-11-15

No in truth it is still an 8 bit system as it display any of 256 values using 8 bits.
It is most definitely not 256 bytes, bits and bytes only refer to the number of digits used for storage or display not the max values although they are related.
256 bit graphics is also wrong terminology it is 256 color mode or 8 bit graphics.

author

It is a little fast in the video but not for me I analyze circuits in my head faster than most people can build them in an electronics program somthing I learned before computers were common.

author

Didn't say it was too fast, just that it's terrifyingly confusing.

author

It is a bit like learning French don’t try to read it all at once.
The jk flip flop is negative transition so LED 2 turns off and LED 3 turns on when LED 1 goes from high to low only.
Then you move on to the other outputs.
This does the same job as the logic analyzer that is first prize in the hack it contest just not at run speed and for a lot less.

author
agis68 (author)2012-11-15

is very good idea but how useful is an 8bit analyzer?

author
Josehf Murchison (author)agis682012-11-15

When you build a circuit like the Modified sign wave signal generator there are very specific internal high/low signals you need to make the circuit work the way you want. This circuit tells you if you are getting those high/low signals.

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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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