Help buying an oscilloscope

Thread Starter

adam555

Joined Aug 17, 2013
858
I made a pretty cool power supply from scratch as a project in my first electronics course. :)

I'm really thinking on doing the same with the function generator. I think that as soon as I get an oscilloscope that's going to be the first project. I'm getting a bit saturated with theory, and need to so something practical and useful.

What do you think of the diagram I posted above; the one with the 8038?
 

Thread Starter

adam555

Joined Aug 17, 2013
858
OMG! Look what I found: a function generator with just a 555!



I'm going to try it straight away. :)

If it works, that will be my function generator. :D
 

THE_RB

Joined Feb 11, 2008
5,438
If you wanted a step up from that, this one has xtal-locked exact decimal Hz frequencies, with high stability and high waveform accuracy of the sinewave;



http://romanblack.com/onesec/SineDDS.htm

The HEX code is provided to program the PIC chip, but of course you may need to build or borrow a PIC programmer.

It also makes square/saw/triangle waves.
 

Thread Starter

adam555

Joined Aug 17, 2013
858
Thanks, while I was looking at the diagram of the one with the 555 I realized you can't change the frequency; am I correct? :confused:

I can see you can change the output level with the RV1 pot, but can't see what's controlling the 555.

About yours: that's a Pulse Width Modulated sine wave; isn't it? I'm not trying to be difficult to please, just wondering if PWM would be good for all uses.
 

Thread Starter

adam555

Joined Aug 17, 2013
858
Thanks; I was guessing R7. :)

But, changing just the resistor will not completely adjust the frequency; just change the period of time the cycle is down. Don't you need to change both the resistor and the capacitor in a balanced way to have both semicycles synchronized?

Just tested it in a simulator, and the waves look nowhere near what they should; except for the square wave, which is basically what comes out of the 555. It could be because I couldn't use the exact same transistors, but I think I'm going to pass on that particular design. It's not something I would like to keep.
 
Last edited:

Austin Clark

Joined Dec 28, 2011
412
Make a digital to analog converter out of resistors, and feed it values from the parallel port or from a microcontroller. It's surprisingly easy to do, and you could create literally any waveform, and you could use an adjustable amplifier on the output to adjust amplitude beyond 5V.

I connected a counter to a DAC I made once, and made a super simple ramp generator.
 

Thread Starter

adam555

Joined Aug 17, 2013
858
At the moment I wouldn't be able to come up with a circuit that does that. But I was thinking something similar: do it by software through Arduino. Problem is, it would be PWM.

Been looking through circuits and most use the 8038 or the XR2206 function generators -and I was really keen on doing it as a serious project-. Unfortunately, neither my local shop nor Digikey (which I was planning on making an order) sell those models, nor any equivalent that I could use. :(

Looked other designs, but above those they all get to complicated for me.
 

DerStrom8

Joined Feb 20, 2011
2,390
At the moment I wouldn't be able to come up with a circuit that does that. But I was thinking something similar: do it by software through Arduino. Problem is, it would be PWM.
You could set up a low-pass filter on the Arduino's PWM output to filter out the high frequency PWM signal, and leave only the lower frequency output. Your frequency range won't be great, but it might still do the trick.
 

Thread Starter

adam555

Joined Aug 17, 2013
858
I knew there was a way to get rid of the PWM; but couldn't figure it out yesterday. :p

For a trial and as an emergency FG would be fine. However, what I don't like about that project is that I would be doing it all with software, and getting practically no experience with electronics.

I'm also sort of looking to make a function generator that I can add to my tool kit; something that I'll always be able to use to test my projects. Well, you know, something worth keeping, like the Power Supply I made. But just can't find a design that would do, and which I'm able to get the parts.
 

Thread Starter

adam555

Joined Aug 17, 2013
858
I'm really considering that option... and I guess at the end I will end up buying one of those. The quality and accuracy is not really important; I'm only going to be using it for tests and experiments... and not that often.


For now I still have the hope of finding a fairly good and simple circuit that I can do at home; or figure out how to design one myself with a 555 timer (can't be that difficult :p)
 

Thread Starter

adam555

Joined Aug 17, 2013
858
I'm near winning one of the oscilloscopes, which comes with nothing else; just the device. It says: *NO ITEMS, PODS, PROBES, STAND, CABLES OR ANYTHING ELSE INCLUDED

I'm about to make an order to an electronics shop, so I'm wondering -apart from the probes with cable; what else should I buy for the oscilloscope?
 

Thread Starter

adam555

Joined Aug 17, 2013
858
OMG!!!!

€25 for the cheapest oscilloscope probe in Digi-key!!!!!... that´s what I´m paying for the whole oscilloscope. :D
 

Austin Clark

Joined Dec 28, 2011
412
I'm near winning one of the oscilloscopes, which comes with nothing else; just the device. It says: *NO ITEMS, PODS, PROBES, STAND, CABLES OR ANYTHING ELSE INCLUDED

I'm about to make an order to an electronics shop, so I'm wondering -apart from the probes with cable; what else should I buy for the oscilloscope?
A power cable if you don't already have a spare one.
If it's a dual channel 'scope, you'll want two sets of probes.
 

Thread Starter

adam555

Joined Aug 17, 2013
858
A power cable if you don't already have a spare one.
If it's a dual channel 'scope, you'll want two sets of probes.

Found a pack of 2 on ebay from China for £7.

Hmmm, doesn't look to bad at all.
It even looks easy enough for me to reverse-engineer, and learn how it works! :)
If you reverse-engineer it, please send me the diagram. :)

I was also trying to find the IC to see if I could find a similar circuit, but I can't see it on the pictures. I it looks like a DIP8 format IC is connected under the the LCD, but that can't be all; I suppose that it has to have at least something else under there to control the screen menu and output.
 

Thread Starter

adam555

Joined Aug 17, 2013
858
Hmmm, doesn't look to bad at all.
It even looks easy enough for me to reverse-engineer, and learn how it works! :)
Austin, just bought 4 x 8038 ICs for £3,50 (saw them this morning elsewhere for $60 each!); if you want one to make a function generator let me know.
 

THE_RB

Joined Feb 11, 2008
5,438
Been looking through circuits and most use the 8038 or the XR2206 function generators -and I was really keen on doing it as a serious project-. Unfortunately, neither my local shop nor Digikey (which I was planning on making an order) sell those models, nor any equivalent that I could use. :(
The circuit I posted far exceeds the performance of the 8038 or XR2206, but is
limited to 20kHz max.

Ebay has some "function generator modules" ready made, that are reasonably cheap and will work straight out of the box.
 

Thread Starter

adam555

Joined Aug 17, 2013
858
The circuit I posted far exceeds the performance of the 8038 or XR2206, but is
limited to 20kHz max.
Yes, but I don't have a PIC programmer or know anyone who does. :(

This one is very simple for me to understand, mount and use; and according to the datasheet the 8038 will work up to 300Khz and outputs the 3 waveforms. It will also cost around £1 each.



Ebay has some "function generator modules" ready made, that are reasonably cheap and will work straight out of the box.
I'll probably end up buying one of those too...
 
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