Advice/Help needed with Digital Integrator Circuit Project.

Thread Starter


Joined Oct 23, 2016
So I need to build a Digital Integrator by around May next year. Most of the classes I've taken are Analog based, so I have little background in digital design. Though I like a good challenge.

The prompt for my project can be found here:

Now I am by NO means asking for someone to do this project for me. Obviously. I could just use a few words of advice, and I have tons of questions to ask since my prompt is very vague.

The basic components of this Digital Integrator are composed of: an 8-bit Up/Down counter, 8-bit adder, and an 8-bit register. As far as I can understand, the 8-bit U/D counter counts up when the input is Positive, and Down when the input is negative. That count gets added into a register and feedback to be added with the next count to accumulate an integral. I plan to use 7400 series IC's, unless anyone else has any better suggestions.

I found this program called Multisim that is available for use at my school, and I think I plan to use it to test my designs. The interconnections of the IC's are troubling me, though. Even after looking at datasheets for these IC's I can't determine what a lot of the pins are for. For example, the EOC pin on the ADC in multisim. I also am not sure I 100% sure how my circuit is supposed to work regarding the inputs. I know I need to load in the initial conditions into the counter using a switch, but I'm not sure what my input signal is going to be, or how to make an initial condition of 32 with a switch.

Let me just ask some questions to keep this organized:

Question 1: Here is my first design of the basic 8-bit integrator,

and my output:

How can I debug this circuit? I am getting basically a flat line as my output, and I'm not sure where to start debugging it.

Question 2:

Are there any major flaws with my circuit?

Question 3:

What is the difference between the normal ground, and the reference ground in Multisim? (Same goes for VCC and Regular Power Supplies).

Question 4:

Are there any good 8-bit IC's I can use to replace the 7400 series ones? I think that would simplify my connections a lot.

Any advice or help you can possibly give would be greatly appreciated.


Joined Mar 14, 2008
Q1: I believe Multisim has a digital logic analyzer.
Connect the outputs of the various circuits to the analyzer to see which ones are working and which are not.
Troubleshooting digital circuits can be tedious.

Q2: Can't advise you on that.

Q3: Didn't know that Multisim had two grounds. Do they have different symbols?
VCC is just a power supply with a fixed voltage and the negative side connected to ground.

Q4: Don't think there's a lot available in 8-bit IC's.
The 7400 series has more different digital ICs available than any other IC family.

Thread Starter


Joined Oct 23, 2016
So I tested each output with what I assume is the digital analyzer, I found out that I needed to connect my U/D Counters to a load to enable my 0000 IC. That got me outputs from the counter, and the counters seem to be working correctly. When the count goes into my 8-bit shift register on the far right, everything drops to 0. I tried connecting a circuit to clear the register, but it doesn't seem to get me anything to store in the register. I tried switching the operation mode of the register, but that didn't help at all either.

Any idea on how to get an output out of the shift register U7?

Here is my new circuit, with the digital analyzers displayed:

Edit: Switching the mode of operation to 11, now gets me an output in the registers.
Here is my output waveform:
It looks very random, and I'm not sure where to go from here. Ideally it should be close to a cosine wave.
Last edited:

Thread Starter


Joined Oct 23, 2016
Update: Here are different outputs of the circuit at different frequencies of the circuit:

It seems like it could be an overall design issue. The circuit is intended to count up when the input signal is positive and vice-versa. When the MSB (D7 of ADC) of the input is positive, it goes to an inverter into the U/D input of the counters. Would this not achieve integration? Is there something else I'm missing here?

Thread Starter


Joined Oct 23, 2016
So I need to build a circuit that operates according to this block diagram and explanation:

This is how I think the circuit should work:
1. Put an input signal into an ADC, check the MSB to see whether the input is positive or negative, and count up if it is positive, and down if it is negative.

2. The 8-bit count gets added into a register, with whatever is in the register.

3. The register is outputted into an 8-bit DAC, and the output should be the integral of the input.

Am I anywhere close on this? I'm not sure I fully understand how the circuit should work. I made a design for the circuit in multisim, but my output doesn't look quite right.

Here is the circuit I designed:
And output:
My circuit uses an adder to determine wether the input is + or -, and that gets fed into my cascaded 8-bit Up/Down counters. That count gets inputted into a cascaded 8-bit adder, and the feedback from the 8bit register is added with the count. The output is fed into a DAC and shown on an ocsilloscope.

If you could explain to me how this is supposed to work practically, if I'm WAY off, that would be amazing.