Let’s think about this scenario:
It is a Sunday, close to midnight, and you haven't finished with that circuit you need for your Digital course lab for tomorrow morning.
Hours later, tired but finally with the final circuit done on your breadboard (i.e. proto board) and... The logic is not right, the LED should be ON now...but it's not...the true table is right, you "de-Morgan-ized" (I love this word) correctly, you double checked the logic with a simulator... but the logic is still not right. So, time to troubleshoot. You think that you wired incorrectly your logic gates but no, they are right. Could they be damaged? How do I know for sure? What was the true table for the XNOR gate again?
Wonder no more, I bring a solution to you. Sadly, you will have to work for it but, I promise that at the end, this project will do your assignments in no time.
I present you the Boolean Testing Unit (Yes, I know what a logic probe is).
I had this idea after dealing with remembering the truth table of each gate, struggling trying to read the incredibly small close to invisible text over the IC, and trying to figure out if I made a wrong connection when the output logic was making no sense.
It took me a couple of months to design and test it. That was because I didn’t spend too much time working on it (I was taking a summer semester at my college at the same time). For you, I think if we gather the proper components and you dedicate enough time to finish it, it should take you around 2 days to finish it completely.
By the way, it has its own voltage regulator, so don’t worry about that part either. Isn’t that awesome? Lets start.
Step 1: Step 1: Materials & Components
What you will need can be seen in this picture. I forgot to take individual pictures so, that one is on me. Sorry!
Because I wanted it to me versatile, I divide this project into two modules: The Voltage Regulator Module (V.R.M.) and the Testing Module (T.M.). I do not like to use complex components (such as micro controllers, for example) because I wanted to keep it with material you'd be able to find at your electronics shop or your college/university storage location. K.I.S.S. all the time.
Enough, lets start:
- The soldering Board
I bought mine at my local electronics shop, so I'll give you three alternatives you can use to buy yours. If you don't like them, feel free to use any board you feel comfortable with.
- For the Voltage Regulator Module you will need:
- 1 1N4006 Rectifier Diode.
- 1 LM7805 Linear Positive 1A Voltage Regulator.
- 1 470 nF Electrolytic capacitor (i.e. polarized, be careful).
- 1 100 nF Ceramic capacitor.
- 1 220R (Ohms) carbon composite resistor (i.e. the "classic" resistor).
- 1 Green LED.
- 1 clamp connection.
- 5 male pins. (You can buy strips with around 20 of them, and just cut them accordingly).
- 2 2-pin female jumpers. (if you have access to an "old" computer, you'll be able to scavenge anough for the complete project).
- TO-220 Heat sink *optional* (I don't think you will need this one but it makes the circuit look cool. Don't forget the paste tho'.
- For the Testing Module you will need:
- 2 14-pin (7 x 2) IC sockets.
- 4 220R carbon composite resistors.
- 4 Green LED's (you can use any color you want, the brightness may change a little bit)
- 21 male pins (as mentioned before, its easier to find strips with a lot of this that you can cut).
- 8 2-pin female jumpers
- 4 Stand offs with screws (To make it tool-shaped, the size doesn't matter)
- Cutting tool (which ever you want to use).
- non lead Soldering wire (Yes, this is a soldering project).
- Soldering gun (How are you supposed to solder without one?).
- Air filter (or be ready to avoid breathing toxic gases from the solder paste).
- Unsoldering pump or solder wick (for those tiny mistakes that might happen).
- Lots of electric / electronics wire (AWG # 16 is the one I used I think).
The final cost would depend in how much components you actually have to buy (they are all easy to find and take from old circuit boards) and your local retail cost (are you sure the lab supplier cannot give you most of them for free?).
"So, why do you need all these components again?" Thanks for asking!, let me give you a quick review.
Step 2: Step 2: What Is Going On?
The yellow area (on the picture above) shows the Voltage Regulator Module; the green area, the Tool itself.
Voltage Regultator Module
The voltage regulator will give you the Freedom of connecting any (reasonable) DC voltage input to the module and the regulator will be able to give you the 5V your circuit needs to properly operate. If you want to identify the maximum voltage you should connect before bad things happen, here's the datasheet.
Now, can you take a look what's between the clamp connector and the Voltage regulator? Yes, is the rectifier diode. This diode will protect your circuit if you get distracted and connected the voltage source backwards. The 1N4006 are pretty robust in my opinion, but feel free to use any rectifier you want. The price to be payed is that this will give you a small voltage drop that you will have to consider when applying your input voltage.
As a rule of thumb, keep your input voltage 1.5V above the output voltage you want: We need 5V on the output, so choose an input voltage that will give you
5V (desired output) + 1.5V (buck) + 0.7V (Diode voltage drop) = 7.2Vdc
If you experiment with your source voltage (input) you will notice that with lower voltage levels your circuit will start to operate. Yes, it will. But, you may lack power to feed your circuit; you make the call.
The jumpers were included to make the design a little bit more versatile.
- The top jumper will separate the modules so you can either feed a different circuit with 5V from your module, or feed your testing module with a different source. Not sure why, but you can.
- The bottom jumper will work as a switch so you can leave a fixed voltage source connected to the circuit without having to get the screwdriver every time.
The module that makes the magic. Both sockets are added so you can connect different I.C.s for testing. The top one is dedicated to a NOT gate I.C. and the bottom one to any other 2-input quad gate I.C.
Yes, you can connect a NOR gate too. How? IF you take a look at all the pin configuration of the logic gates, the NOR is the only one that does not follow the same sequence, right? but if you are a good observer (which I know you are) you will notice that all the pins are just upside down. So, my tool gives you the liberty of connecting this gate on the other orientation. The only thing you MUST do is to switch the jumpers next to the socket.
Another feature I included to my tool is the ability to switch between direct output and inverted. As I mentioned before, you have a NOT gate socket, correct? Well, you can either choose to test the gate directly (by not adding any other gate to the bottom pin and observe the outputs) or use this gate to invert the output logic of the I.C. being tested.
Don't worry, this was just a description, now lets take a look at the schematic.
Step 3: Step 3: the Schematic
I uploaded the schematic so you can download it to Visio (That's the one I had access to). IF you don't want to, I added a picture of it. I think its pretty easy to follow. The only thing that changes between the schematic and the final product I made is the location of the I.C.'s. I didn't relocated them on the diagram so its easy to follow the logic (I hope...).
You can arrange the circuit in any position you want, I'm only giving the one I used. As you can see, no fancy components were used.
Remember, the "triangles" at the bottom are the equi-potential connection, or common ground for the circuit.
I added some labels within the understand to help you understand what each groups of pins will be doing for you:
- P01 - Jumper to be used as the power switch.
- P02 - Jumper to connect modules.
- P03 - Jumpers to be used to enable/disable I.C.s (cut off power) and select logic combination.
- G - Jumpers used to switch power for just one of the gates.
- NOT - Jumpers that will give select between direct output or inverted.
Before anything bad happens, this are the gates that were tested and the purpose of this project:
7400 - NAND gate
7402 - NOR gate
7404 - NOT gate (i.e. inverter)
7408 - AND gate
7432 - OR gate
7486 - XOR gate
The family or technology you want to use is OK as long as the pin out stays the same.
SO...The logic is there, the schematic is there, what's missing? O yeah, Lets start already!
Step 4: Step 4: Layout & Soldering
I don't have sophisticated software to work so I work with what I have: Excel in this case.
This is a rough description of where I located each component (Described at the materials' step) within the soldering board I got. If you don't have a board like mine (21 x 15 pins), your project might differ a little bit from mine. Because this is D.I.Y. projects' website, I'm sure that's suppose to happen anyway.
This is the ugly part. I cannot give you "the best way" to solder the components to the board, for each one has its unique technique. IF you have access to a copper board and you want to do your own custom board, please go ahead. You can make your own printed circuit board? Please, by all means.
I will do my best and give you the "theoretical lay out" I wanted to use. But, as you will see in the actual soldered layout, I ended up working on the go. The grey areas are the soldered pins. Sadly, the board I used didn't work with me as I was expecting, plus I was starting to practice my soldering skills at the same time. You will notice a transition of soldering skills in the last picture...
I had to make layers with the wire because the board I used has nothing interconnected by default.
I used different colors to keep a color code depending on what each wire will do for me (see final layout). This is the code:
- Red – supply voltage / logic 1
- Black – reference / logic 0
- Yellow – Logic output to P04
- Brown – Logic output to NOT input
- Purple – NOT output to P04
- Blue – discarded
Good luck on this step!
Once you have done, lets check if everything is right. Do you have a NOT gate and any of the other logic gates to be tested? lets use them.
Step 5: Step 5: How to Use Your Tool
Lets go in order to avoid getting *more* confused.
Pins P01 and P02 are easy to follow.
Lets take a look at the Power selection arrangement P03. This arrangement is designed (if you connected as shown on the schematic and my layout) to avoid unwanted connections. IF you take a look at the picture for this group (P03):
- Using only one jumper as indicated in a), you will power your logic I.C. but not the NOT gate.
- Using only one jumper as indicated in b), you will power the NOT gate but not the other logic I.C.
- Connecting both jumpers as indicated by c) you will power both I.C.s. connecting the circuit in a different way will not power any of the I.C.s
Oh, that additional pin (k)? That's a leftover from my prototype. It was too late for me to remove it and you can use it to keep one of the jumpers within the circuit so you don't loose it (See? I think in everything!).
Lets talk now about the pin arrangement G. This pin out will switch the power delivered to the logic I.C. (i.e. the input voltage will switch to the common ground, and vice versa). Take a look at the picture for this arrangement:
- Connecting the jumpers as indicated in a), you will power all the logic I.C.s except for the NOR gate.
- Connecting the jumpers as indicated in b), you will power the NOR gate but not the other logic I.C.
NOTE: This is the weak link of my project. I do not added any current protection or inverted voltage to the testing module (only the ones integrated to the LM7805), please avoid:
- Connecting a NOT gate to the wrong socket. The top socket (as seen on my diagram) is designed for this gate.
- Remember the only IC that needs arrangement G-b is the NOR gate (7402), all the others are arrangement G-a.
Lets talk about the Direct/ Inverted pins' lay out (P04). This pin out will give you the option to display the direct output of your logic I.C., or its inverted output. Why would you do that? why not!:
- Connecting the jumpers as indicated in a), your output will be DIRECT.
- Connecting the jumpers as indicated in b), your output will be INVERTED.
Well, and that's pretty much it. Congratulations, you have done a *takes deep breath* fully operational 2-input quad logic gate I.C. tester with integrated modular voltage regulator. Let's see it working.
Step 6: Final Step: Evidence
I'm adding a bunch of pictures testing different I.C.'s and pin configuration.
Also, I wouldn't be telling you that diode helps without trying it myself. Notice the funny looking power supply giving a little bit more than 15Vdc inverted to the tool without damaging it (Yes, I have used it after testing this function). That power supply is a college project, don't worry about it. The display is a little bit off tho'.
If you want to see the documentation I collected for this project, please find the report attached (yes, the pdf). It contains all the collected information, testing, and additional data that I collected from my tests. There's a datasheet within that report that you can use (if you want) for your tool.
IF you think I missed something, there's something confusing, I did something wrong, or any feedback you want to give me, please feel free to do so. This is my first Instructable so I am expecting some details on my writing and explaining. I did my best to avoid them.
Have an excellent day!