PC-based oscilloscope

[mshemyalnisar]

I intend to make a PC-Based oscilloscope, for the reason to be able to work when the lab is closed as well.

the design is simple to have ADC connected with a buffer with is then connected to a parrallel port of the PC. I wanted to know that will it work? and what will be the constraints on it? and how can the design be improved for the purpose it is being made, keeping in view the cost factor

 

[akg]

if ur not using ASIC the range and performance will be very low.

 

[mshemyalnisar]

what kind of ASIC and in what place please explain??

 

[Rolf]

Here is one for free............

I intend to make a PC-Based oscilloscope, for the reason to be able to work when the lab is closed as well.

the design is simple to have ADC connected with a buffer with is then connected to a parrallel port of the PC. I wanted to know that will it work? and what will be the constraints on it? and how can the design be improved for the purpose it is being made, keeping in view the cost factor

This free software PC oscilloscope might do the job for you if your requirements are not to stringent.
Link: **broken link removed**

 

[RadioRon]

A PC scope, like most digital scopes, work by sampling the analog signal and then changing the sample voltages into numbers to be manipulated and changed into a graphic display by the PC. There are certain basic limitations that you will suffer. One of the primary characteristics of scopes is the bandwidth. If the bandwidth of the scope is lower than the bandwidth of the signal you are trying to see with it, then you will not see the signal exactly as it is, it will be distorted. This is bad. So the bandwidth of the scope is often used to describe the overall performance, even though there are many other factors. Let's talk about bandwidth of a PC scope.

The bandwidth you can get will be dependent mainly on the sampling rate you can use. This rate, in turn is dependent on what A/D circuit you use, and whether your PC software can collect the numbers from the A/D and then display them fast enough to not lose any of the numbers. I'm not sure, but i believe that the A/D capabilities of a typical Sound Card, for example, are only suitable for high fidelity audio, which translates to rates on the order of 30 to 100KHz. You should learn the Nyquist principle which rules that you typically will require a sampling rate twice as high as the maximum frequency you want to see (which is the same as twice the bandwidth). So, if you wanted a PC scope to display signals with frequency content up to 10 MHz (which would be a useful scope) you would need a sampling rate of 20 MHz.

As I mentioned, the sampling rate is something that drives your choice of A/D circuits and also is limited to how fast your PC software can go. The way that you interconnect the A/D into the computer may also limit the sampling rate. For example, there will be a maximum data rate that you can achieve using a parallel port. I'm not sure what the limit is, but it is reasonably high from the hardware point of view. However, if you access the parallel port through the Windows operating system you may find that the OS cannot go fast enough. Perhaps your program could access the parallel port directly for faster speed.

You ask:
"and how can the design be improved for the purpose it is being made, keeping in view the cost factor"

This is difficult to answer since you did not state the purpose of the scope nor have you stated the cost target. Can you add more please?

 

[Analog]

I think EDN had this circuit a while back - might be worth a search.

 

[mshemyalnisar]

the purpose that you asked for is simple that i dont have to go to lab to work on something because i hate to adjust myself with the timings of the lab. So all i need is something that would the serve the purpose and my need to go to the lab so i certainly can work at anytime of the day, whenever i want.

So the cost thing should not be so high as being a student i shoud be able to afford it.


another thing that i got this as a lab assignment back at the beginning of the semester, at that time we gave the input using function generater and it worked to the level of the satisfaction of our lab instructor.

another thing that can to my mind was that what if the signal goes above the TTL-level of 5V what should i do i that case. an idea that came to my mind was to make a voltage dividor network and then take the voltage from there. so would this idea work??

i really appreiciate your advice people thanx.

 

[kinjalgp]

Check out some of these hobbyist projects,

**broken link removed**
**broken link removed**
http://alternatezone.com/electronics/dsoamk3.htm (Parallel port based)
http://www.johann-glaser.at/projects/DSO/
http://www.bitscope.com/ (Old Schematics are availabe for download)
http://www.fpga4fun.com/digitalscope.html (FPGA Based)

 

[RadioRon]

the purpose that you asked for is simple that i dont have to go to lab to work on something because i hate to adjust myself with the timings of the lab. So all i need is something that would the serve the purpose and my need to go to the lab so i certainly can work at anytime of the day, whenever i want.

So the cost thing should not be so high as being a student i shoud be able to afford it.
.

Thank you. You bring a smile to my face with your answers. Please take no offence because none is intended and indeed your answers are absolutely correct. Its just that they remind me of the classic conversation between the engineering guy and the marketing guy as they define their company's new product. The engineering guy wants to know how big it should be and the marketing guy answers "imposingly big". Then the engineering guy asks what it's purpose is and the marketing guy says "to sell to customers of course". Finally the engineering guy asks how much it should cost to make and the marketing guy says "no more than 50% of what it will sell for!"

I'm sure the old experienced hands here will recognize how difficult it can be to design products in some companies. Too many Dilbert moments.

I'm sorry if you don't get the joke, and I apologize for wasting your time. By your answers I must guess at the necessary performance of the PC scope you wish to make, and also must guess at the cost to make it. But, being used to that sort of thing its not a problem, really.

 

[mshemyalnisar]

the joke went over by head, anyway i didnt quote any cost limitation because i live in pakistan and none of you probably lives anywhere near therefore there are price differences of electronic components. there are many things that are not even available here, last semester i needed a module that had a retail price of $20 but when shipment and stuff was included the price went up to $80. this module was not available in the local market.

BUt if you really insist then he price should not be go beyond Rs. 1000. the conversion rate is : US$1=PKR60.62

simply logic gate ICs are available @Rs.15
8051 controllers are available @ RS. 70
ADCs @Rs. 25

and other stuff is somewhat in that range.