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Anyone have a recommended inexpensive oscilloscope for debugging HP calcs?

Is 1Mhz bandwidth sufficient?

Edited: 29 Aug 2010, 10:37 p.m.


'Inexpensive' is different according to the purpose.
1MHz bandwidth is not sufficient except some audio applications.

Expressions to choose an adequate oscilloscope from signal-bandwidth are,

1. Signal-BW(band width) = 0.5 / rise-time

2. Oscilloscope-BW >= 2 * Signal-BW

3. Oscilloscope-sampling-rate >= 4 * Oscilloscope-BW

If you wand to measure a circuit operating at several MHz of system clock and its rise-time is assumed to be 10ns,

1. Signal-BW = 0.5/10ns = 50MHz

2. Oscilloscope-BW >= 2 * 50MHz = 100MHz

3. Oscilloscope-sampling-rate >= 4 * 100MHz = 400Msps



I have a feeling that you're asking about one of those very inexpensive USB 'scopes or one that's built into a DMM. Mostly what you need to work on digital electronics is a logic analyzer, but given that most vintage calculators were bit-serial devices you don't need too many channels, just one to watch the signal line and a couple of others to watch the handshake lines. Also an oscilloscope will let you debug problem power supply lines and such while a logic analyzer won't help at all in that regard.

If you're only interest is in old HP LED calculators the clock speeds were pretty slow, you could just barely get by with a 2MHz 2 channel 'scope, but 4 channels and some more speed would be most helpful. I wouldn't recommend anything less than 5MHz. Some of the low cost USB scopes have 2 analog channels and 8 digital ones (these are usually referred to as a mixed signal oscilloscope or MSO). They might be a good compromise. Here's one such device but you should read the reviews of this.

However, I find that there's nothing as good as having a dedicated digital oscilloscope of some sort on your workbench, it defiantly beats a USB scope feeding a computer for ease of use. You also want to look for one with a lot of memory depth so that you can scroll around and see the history of the signals you capture.

This is the one I've used for many of my embedded projects, and it's a beautiful device. Works great too! ;-)

Portable oscilloscope

I highly recommend it.

For the logic analyzer side, I chose this...


...after a long period of research, which included comments and opinions from many on this forum. The second choice unit was this one:

Saleae logic analyzer

I ultimately chose the USBee unit because of the software, which I thought was better. Plus, it had some nicer features in the hardware design (external trigger). The Saleae unit was a very close second, though -- it's a beautiful device too.

Now below is another interesting new product with many functions built in, and it would be great for many embedded projects:




Anyone have a recommended inexpensive oscilloscope for debugging HP calcs?

Is 1Mhz bandwidth sufficient?

Define inexpensive.

Define what you want to "debug"

If you just want to see if a signal is there or not then a 2nd hand 20MHz or so analog oscilloscope is just fine.

If you want to capture and debug signals then a USB logic analyser is a better bet.

If you want a "real" digital storage bench scope that is excellent value for money with a deep sample memory. Go the Rigol DS1052E. I have a ton of info on it on my site and the EEVblog forum.


But I *DO* have a "real" oscilloscope as well. A nice color Fluke 100MHz with all the bells and whistles. I just don't find the need to bust it out all that often. When I do, it's nice to know it's there, but 90% of the time the little one is sufficient for my small projects.

And, it's important to recognize the difference between someone who NEEDS a full-blown oscilloscope and sits in front of one all day (like Dave here! ;-), and someone who just putts around in the embedded world from time to time (like me). With that distinction, I stand by my original recommendation (but, of course, I respect yours too, Dave ;-).



I bought an old Tektronix 2235 100MHz 2 channel analog scope off TAS for about $200 many years ago. It has served me well in debugging the Classics.

I'm using a Hameg 605 from 1984. A 20MHz model would be sufficient for the classics, though.