Author Topic: Setting up a bench ...  (Read 263 times)

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Offline mossygreen

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Setting up a bench ...
« on: June 21, 2021, 02:47:27 am »
I thought I'd share some thoughts about my experience setting up a "bench", in particular w/r to instruments. I know a tiny fraction of what others on this forum know but I think that the perspective of a newbie (although an old one) might be helpful to other newbie's.

When I first started to try and learn something about electronics I read posts, watched YouTube videos, read articles from publications, etc. I ended up with a few good solid DMM's (Fluke, Brymen, 121GW) and some older equipment from the bay. The meters are great - always useful in orienting myself to a circuit in operation. The older equipment was a bit of a mixed bag. I don't have anyone around me to ask and without "known good" units it is very hard to know when something is working or not. Poor measurement methodology can trip up most people at least some of the time. I've slowly been acquiring choice bits of gear that let me understand the older stuff.

One thing that was a real win - I picked up a Tek 2465B that was in great shape and cal'd. I had enough confidence in that scope that I persevered in learning to use it - and learning an analog scope is a great foundational exercise. I also picked up a very inexpensive digital scope that I used for use cases when the Tek scope wasn't a good fit (e.g., slow stuff). My 8yr-old daughter asked to learn how to use a scope this summer and I'll be teaching her on the Tek - quite frankly it really helps you understand what is at least logically going on.

Recently, I built one of Ben Eater's clock modules and as he alludes to in a later video there was a challenge in how well debounced the manual clock was. The circuit is so slow that you can't use the 2465B with it ... but the cheap computer-based scope helped. However, after I fixed that problem (by slightly lengthening the 555 timer delay on the manual pushbutton) I had a nagging sense that something still might not be right. I tried logging with the inexpensive scope, etc., but there appear to be occasional glitches where the logged data shows a near-zero value. Now, I'm sure that if I had someone to talk with that knew the ins & outs of the inexpensive scope I could become satisfied that my updated clock was good to go - but I didn't. I had, however, spent enough time with each to know that I prefer to operate an instrument on the bench as opposed to a computer.

I spent some time looking around and ended up with a R&S RTB unit that I got to spend some initial time with this weekend. Apart from (re)discovering that separately acquired 400MHz fixed 10:1 probes leave the supplied probes in the shade, this modern scope just nailed it. I was able to look at triggering for clock waveforms that were too short and by playing around with that threshold and using the segmented memory I now have high confidence that my adjustable clock unit is good to go. The 2465B has more BW and I'm certainly keeping that, but a few decades has brought truly useful digital capabilities into the realm of the merely "slightly nuts".

One other item - logic analyzers. If you look around today all the $-approachable analyzers are narrow (8-16 channels) - which is fine for serial stuff and narrow things. Older gear, however, uses wider stuff and some stuff you might (as a pure hobbyist) assemble yourself would be much wider than 16 channels. Well, it turns out that Arduino's make okay *very slow* 50-ish bit wide log analyzers so you can go that route. Wide (and slow) analyzers are readily available used.
 

Offline mindcrime

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Re: Setting up a bench ...
« Reply #1 on: June 21, 2021, 01:42:36 pm »
Quote
Wide (and slow) analyzers are readily available used.

Indeed. I picked up an HP 1660A with 136 channels on Ebay for < $300.00 USD. It's not fast enough for a lot of newer applications, but I doubt that I'm ever - as a hobbyist - going to need more than 136 channels.

I'm also considering picking up a Tektronix TLA 704 or similar at some point, just because A. they're fairly cheap, B. I don't have any Tek kit at the moment, and C. I sort of collect logic analyzers.  ;D


And while we're on the topic of "setting up a bench", if anybody cares for any advice from a guy who's been a beginner for 40 years now, here are a couple of random thoughts:

1. A good bench power supply is worth its weight in gold. I use a Rigol DP832A, but any quality supply should be fine. Some key aspects of a real lab power supply (as opposed to re-purposing an old ATX power supply, etc.) - You get adjustable voltage over a fairly wide range, and down to a couple of decimal points of precision. You can also vary the voltage across multiple channels simultaneously, which comes up more often than you might expect. Needing say, a 3.3V rail for logic "stuff" and simultaneously needing a 12V rail for powering an actuator or something. And having a 3rd independent channel really gives you a lot of flexibility. The other big things are a constant view of current on a given channel (how many times have you wanted to know how much current a component or subassembly was really drawing) AND current limiting. It's nice to be able to preset a current value and know that you can connect something to the supply with no fear of blowing something up by dumping too much current into it.

2. I'm a software guy and a data/analytics guy by trade, so I may care more about this than other people, but I think a really important factor of test equipment is the ability to interface with it from a computer and log data. I make it a point to always buy gear that has either an Ethernet port with LXI, or a GPIB connector, or worst case, plain-old RS-232. This whole thing is one reason I try to keep the number of brands of gear I use to a minimum (I use almost exclusively Rigol and HP/A/K kit). It's well known that LXI and other protocols aren't always implemented consistently across manufacturers, so I wanted to be able to fiddle with an open source library or what-have-you, get it working for manufacturer X and then mostly not have to worry about it.  I have a separate PC that I use for data logging from instruments and I will eventually move that, and all the test gear, to an entirely separate network segment or VLAN within my network, just to keep things neat.

3. I regret waiting as long as I did to buy a proper temperature controlled soldering station. Once you get one, you'll never want to touch one of those cheap Radio Shack "pencil" soldering irons again.

4. I'm not convinced that it's important to use expensive solder, but I will argue that it's important to keep different sizes of solder on hand. I find that using the appropriate gauge solder makes a big difference, and it really does vary depending on what you're doing. Outside of that factor, I haven't found that using 60/40 vs 63/37, using silver bearing or not silver bearing, using multi-core or not, etc. makes a huge difference. I keep solder here from Multicore, Kester, Chipquick, and even some of that exotic stuff that contains silver, copper, and FSM-knows-what-else, and I still find that I reach for an ancient tube of Radio Shack 0.31" silver-bearing solder more often than about anything else. YMMV. *shrug*

5. Additional flux really does seem to help though. I keep a bottle of MG Chemicals flux and an eyedropper handy, and often apply some flux directly to whatever I'm working on. It really helps, even when using the "nice" Multicore solder or whatever.
« Last Edit: June 21, 2021, 05:17:40 pm by mindcrime »
 


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