OT: Bargain eBay Oscilloscopes

Tom2000

Senior Member
I bought a cheap scope on eBay five or six years ago.

At that time, the Tektronix 2235 (which I bought) was "THE" bargain scope. There were a bunch of them, all going for very good prices. 100 MHz, dual channel. Built like a tank.

That scope has been a real workhorse for me. It's been a great bargain.

Although I don't plan to buy another scope in the near future (unless this one breaks, which it shows no sign of doing), I took a quick peek on the US eBay site to see what folks are getting for used Tektronix scopes these days.

I was very surprised to see that "THE" scope right now seems to be the Tektronix 2465, a 4-channel 300 MHz microprocessorized machine. There are a bunch of them listed. It looks like they'll also go for very good prices.

Five or six years makes a lot of difference!

Tom
 

moxhamj

New Member
Agree - great prices. I just bought a scope last week - been saving up for the last 20 years! It has made a huge difference debugging a range of circuits that never worked properly, some of which were even harder to debug as the PC soundcard scope introduced its own errors. Definitely buy a scope if you can afford one.
 

Fletch

Member
Is there a PC hosted solution that sits somewhere between the soundcard and a dedicated scope? I live in an appartment and can best be considered a "kitchen table" tinkerer. A few years ago I bought an older HP logic Analyser that I have used a total of 4 times, the thing is simply too big and bulky to be an everyday tool, I find myself using it only when I'm completely stumped. Recently I have been very tempted by the USB based LA some folks posted here. Is there a similar DSO product available?
 

andrewpro

New Member
There are a lot of pc based DSO's out there. The above mentioned picoscope being one. However, I would not recommend the picoscope for anyone who does real work with a scope. And trust me, once you have one worth having, you're going to be a serious scope user.

The main reason for nixing the picoscope: Cant use different probes.

You can get a new pc based scope worth having for about the price of a very nice ebay dedicated one. Just make sure you can attatch your own probes to it. Try to look for one with high speed USB2 connection, too. Theres no point in having a pc scope with 100 msps if it cant move that much data.

--AndyP
 

beny1949

Senior Member
i recently bought a colour graphic calculator from my school. its a casio something.... that is irrelevant, because they all have a serial port which I feel would be wasted if it was not connected to a picaxe!!!

It is quite possible to transfer data to the calculator at 9600 baud. So i think (and tell me if i am deceived) that i could transfer voltage and time from a picaxe to it, as a regularly updated table, which the calculator can draw as a graph. I am aware that it would not be the most amazing piece of scope you ever laid hands on, but i think it could work.

On the calculator side of things, it comes with a complete IDE built into it which you can program to use the serial port, and take full control of all resources. and with 64Kb of program space it does not have to be limited to a small program!

What do you think guys?

Note: the calculator does have a retail value of about 80 squidalies (GBP), but i can get them from my school for £30, hence i have one at all!
 

womai

Senior Member
The Picaxe is just not fast enough for real-time scope performance. The best you can do is some kind of sort-of-fast datalogger. I ran some experiments, using a 28X1, clocked at 20 MHz, and doing hserout at 115 kbits/sec. I.e. that's the absolute top of the Picaxe line speed-wise as far as I can see. It's running in an eternal loop forever, so no overhead for variable increments etcl. All the Picaxe is doing is sampling data on two ADC channels and sending this over the hardware serial port. The receiver (e.g. a PC) would have to do all the triggering (finding out when the signal crosses the threshold), scaling, display etc. Yes you could unroll the loop - limited by the 4k program memory - and make it a bit faster but then you loose the ability to do true reliable pre-trigger acquisition (since you don't know when the trigger will come), or you have a small gap whenever you do have to loop around.

With a scope I measured 1230 samples/sec. You can of course almost double that, to about 2000 samples/sec, if you need only one channel. Still not truly scope performance, but would be good enough to look e.g. at serial data running at 600 baud or less. One could write a simple VB program that would take that data and display it in real time, with option to trigger on rising or falling edge on one of the two channels. Adding a pre-amplifier/attenuator, enclosure, connectors would make it a simple two-channel-scope-like box that one should be able to build for US$20. Good enough and cheap enough for school demonstrations?

If enough people are interested (and I can find the time), I would be willing to develop such a thing - hardware and software - as an open design. So let me know if you want it.

Wolfgang


Code:
setfreq em16
hsersetup B115200_20, %00

myloop:
    readadc10 0, w1
    readadc10 1, w2
    hserout 0, (b2, b3, b4, b5)
goto myloop
 

womai

Senior Member
Ok, I unrolled the loop and reduced it to a single ADC channel.

- with readadc10 & sending 2 bytes: 2650 samples/sec
- with readadc & sending 1 byte: 3520 samples/sec

WOlfgang
 

Fletch

Member
Let's ask a related question. Does anyone know of a small/light scope good for relatively low Mhz microprocessor work that would be cheap surplus. I looked that the Tektronix scope listed above and those are great prices but the thing looks as large and heavy as the LA I have. It would be nice to have one that only takes up part of the kitchen table :)
 

hippy

Senior Member
Topically, I've been working on my Logic Analyser design using 'the spinning thing from the dark side'. Can currently capture 16 digital channels for 400 samples at 50nS ( 20MHz ) and about 5,000 samples at slower rates. Can probably double the samples when slow and a sample time of 12.5nS ( 80MHz ) is technically possible.

No analogue at all, but I normally used a DSO only for digital work anyway, and mostly just to confirm signals are happening, polarity and timing. It's the storage part and pre-trigger display I find most useful for the things I do.

Only display on a TV so far ( 2" LCD is so-so passable ) and no control interface yet; will be PC keyboard or serial to start with. Whether I build any PCB's or not I've decided that I probably will Open Source or Freeware the firmware so for less than 20 GBP / 40 USD that's a complete PICAXE compatible logic analyser available for the taking, but no timescales at present.

I'm still trying to weigh up if I should start with it as a standalone unit or make it PC dependant. Pro's and cons to each. Serial data dump is the bottleneck. Bit-banged ethernet would help, but not quite there with that - ironically I need a good analogue scope to go further with that idea :)
 

w7spy

New Member
Hitachi O-scope V-509 50MHz w/o probe

I have a Hitachi V-509 that's been in storage for years. It was a showroom unit that arrived missing the probe and manual. Will I need a Hitachi probe specific for this scope or can I use an off the shelf probe? Thanks
 

womai

Senior Member
As long as you stick to passive probes (or active probes with external power supply, but that's really not worth the hassle for 50 MHz bandwidth), you should be able to use any probe you want. Just make sure the rated bandwidth is as high or higher as the scope bandwidth, otherwise you'll lose performance. Decent 60 MHz probes typically sell for less than US$20 a piece today.

Wolfgang
 
Top