Hi, we are having a problem with making a binary to BCD converter. The first picture is the converter and the second picture is the add3 circuit. In total, we have used 42 ICs and a lot of wires. When we tested it, all the outputs are always logic 1. We are sure about the connections. We are guessing there is not enough supply voltage for the ICs. We are only using a 5V supply. What can we do to make this work. Thank you!!!!

 

We are guessing that there is not enough current in the circuit since where only using a 5V supply.

If the logic is designed for 5V and you are applying 5V, then it is getting all the power it needs.

What logic devices are you using?

Post a schematic of the circuit including the pin connections along with the power and ground connections.

 

If the logic is designed for 5V and you are applying 5V, then it is getting all the power it needs.

What logic devices are you using?

Post a schematic of the circuit including the pin connections along with the power and ground connections.

We're using 74LS series ICs for this project. We did use 5V as the supply voltage but still the output is always logic 1. So we tried to increase the supply voltage up to 7V but the output is still the same. We thought the reason is that there isn't enough current that passes through the ic's since we used a total of 42 ic's, plus the resistances of the wires are also a factor. What should we do to put enough supply current to each ic for it to work?

 

we tried to increase the supply voltage up to 7V but the output is still the same. We thought the reason is that there isn't enough current that passes through the ic's since we used a total of 42 ic's, plus the resistances of the wires are also a factor.

7V is the absolute maximum operating voltage for those devices.
There's absolutely no reason to go above 5V.

The wire resistance likely has nothing to do with your problem.

How much current is the power supply rated for?
Does it output 5V when the circuit is attached?

Your problem is likely an error in the wiring or logic.
Do you have power and ground to all IC packages?

 

Either wired wrong or that logic gate/chip is fried.

If chip has multiple gates, check other gates to see if they still work.

 

You need step through the logic tree with a logic probe, scope, or voltmeter.

Building the circuit is one skill.

Debugging it is another.

 

The first picture is the converter and the second picture is the add3 circuit.

Did your simulation work?

What are the most and least significant bits in your add3 circuit inputs and outputs?

So we tried to increase the supply voltage up to 7V

You should never guess with the supply voltage. You may have damaged some chips and made your troubleshooting problem even worse.

Troubleshooting is more difficult than designing or building; you need to be diligent and methodical to isolate problems.

 

the second picture is the add3 circuit

The style used for the add3 circuit made it straightforward to determine bit order and the logic looks okay.

1. What is your wiring strategy?
2. Are you doing it in a logical fashion by building and testing each converter block and then connecting them?
3. Are you annotating your schematic with gate designators as you go? Or are you being less disciplined?
4. What number are you using for maximum fanout?

Some comments:

Kudos to whoever drew the add3 schematic. S/he is developing some style. I appreciate the clean layout and the consistent connection order (more significant bits on top and always in that order). That's what made it easy to analyze the logic without being told explicitly which letters were LSB. Further improvements would be to eliminate unnecessary wire jogs (only one!), and to use similar layout for the 3 input OR gates. This is one of the cleanest schematics I've seen from a student on AAC.

I have a couple complaints about the way they appear to be teaching these days. When I was in school, the letter A was always used to represent LSB. When I started using TTL, this was further reinforced by the conventions TI used.

Take for example the 74185 binary to BCD converter:

The A input is the LSB and E is the MSB. Whoever drew the converter schematic could learn something from this schematic. Draw your add3 symbol so you don't need wire jogs.

Another example is the BCD to seven segment display you're probably going to use to display the results:

The first few lines of this table show that the LSB is A and the MSB is D.

From a 74LS160 datasheet, you can see that the A output (QA) is the LSB:

 

So what is the logic family? TTL? CMOS?

Is this Homework?

 

So what is the logic family? TTL? CMOS?

Is this Homework?

We're using 74LS series ICs for this project.

 

Hi, we are having a problem with making a binary to BCD converter. The first picture is the converter and the second picture is the add3 circuit. In total, we have used 42 ICs and a lot of wires. When we tested it, all the outputs are always logic 1. We are sure about the connections. We are guessing there is not enough supply voltage for the ICs. We are only using a 5V supply. What can we do to make this work. Thank you!!!!

It sounds like you wired up a circuit having 42 ICs and only then applied power and checked to see if anything worked.

If your supply voltage is holding at 5 V when all of the chips are powered, it is probably adequate.

Do you have bypass capacitors on all of the ICs?

Are all unused inputs tied to appropriate logic levels?

You really need to test your circuits AS you build them up. Your schematics give you a very nice plan for doing this. You have seven ADD3 circuits. Implement and test them one at a time. Then your ADD3 circuit consists of four channels (one for each output bit), implement and test them one at a time, especially for the first one. For the first one you wire up, check EVERY input combination and verify that all of the outputs are correct -- after all, there's only sixteen combinations. For later ones, select two or three input combinations that, between them have each input and output in both possible states. Then, as you connect an additional ADD3 circuit to the overall circuit, run a few tests to see if it appears to be working correctly.