Posts Tagged ‘workbench’

My Latest Big Project

16 April 2020
open side of pattern generator and serializer

I have been working on my latest project for about a week straight now. It’s finally in a usable form.

This project has several purposes behind it. First, I needed a pattern generator to test LED arrays that would output very ordinary patterns, nothing fancy, just so I could tell if the display was working. Second, I needed the output to be serialized to simplify connection of the display to the signal source. Third, I wanted to use as many old boards as I could, rather than junk them.

This project incorporates about a dozen old boards that were taken out of “dead” projects and gathering dust on my bench. They all had to be re-worked for this project. It also incorporates some older pattern generation circuits as a way of preserving a technology I have not been using recently.

Here is another shot of the project:

new project showing front panel

Here we can see the front panel which has four main knobs, DIN connectors for the serial signal output, and some other controls.

Added Control Systems

This was an ambitious project for me basically because of the additional front panel controls that I would not put on equipment unless it was being used to test other equipment.

Besides the four voltage-controlled oscillators (VCOs) that have been fairly standard in my eArt projects, there is a pattern selector that is implemented by a rotating “click” knob that I got off an old mobile radio. This gives me about 64 different possible combinations using just one knob.

The other thing I wanted to implement was the ability to isolate just one section of a pattern and show only that on the display. For this I used an old 4-bit binary rotary switch that I had laying around (making 16 possible choices) and some comparison logic using the infamous “XOR” (exclusive OR) gate, also known as a binary adder. This gate, basically, has one output (“0”) if the two inputs match and another output (“1”) if the two inputs are different. AND the outputs together (after inverting them), and you see if two binary numbers match for as many bits as you need or want.

As a geeky aside, I made use of the fact that binary AND and OR are complementary functions. Thus, you can accomplish a binary AND on the outputs of the XOR gates without inverting them first (to make a match = “1” instead of “0”) using an OR gate, which then gives you a “0” output only when there is a match (when all inputs are “0”). Invert that, and you get a “1” for a match. In my case I needed the “0” to show a match!

I also wanted to choose between the “legacy” patterns that I built into this project and the “simple” patterns used for test purposes. For this I used a 4-bit selector IC. One can make a “tree” of these ICs and select from as many different inputs as one wants.

I don’t build these sort of control circuits that much, so I had to do a bit of head-scratching along the way.

My bench and a few closeups

The project on my work bench

I don’t photograph my bench that often because it looks so messy. But here we see my current setup with the project and one of my displays on it.

To the left is a small oscilloscope and you can see its two test leads hanging down from little hooks. In the center is one of my numerous parts cabinets. Behind the project is a work light and a soldering iron. Above the light is a digital meter I bought used (highly recommended for an electronics bench) and above that a rack chassis full of power supplies. The supply with the panel lit up is the one I use the most.

my bench power supply

It produces four different voltages, 5, 7.5, 9 and 12. I use 5 volts the most. The panel had room for two meters (eBay specials!) so I can monitor more than one output at a time if I need to. Here it shows my five volt connection switched on and drawing 38 milliamps. With CMOS logic, most of the circuitry draws close to zero power. Most of this current draw is from the oscillators.

The 12 volt meter shows 18 mA current draw. This is from the panel meters themselves. It was easier to power them from one of the four supplies, rather than adding another just for them.

pattern generator set up in demonstration area

Here we see the pattern generator installed in its case and running the same display. This is in the “demonstration” area of my room.

closeup of the panel

There is room for another panel section above the one I used. You can also see the binary rotary switch set to “A” which is ten in hexadecimal.

8 spirals display

Here is “8 spirals,” one of my more colorful displays. All the lights should be lit in this pattern, but you can see that there are two lights having problems.

My Bench Gets and Upgrade

27 September 2015

My work bench may one day be an important source of income for me. In some ways it is already, as that’s how I keep up with electronics, which is partly why I was able to land my current job.

So I have been investing in it a bit. I recently procured a tool cabinet (made of steel sheet metal) to help me get more control over my storage problems. And I have pushed by “tower #3” – the Tower of Power with Bungalow – up to an operational status.

Unlike my previous two towers (see Tale of Two Towers), this one resides in a rear corner of my bench, and only a small desktop unit (the bungalow) is within reach. All the contraption does is supply power for my projects before the boards are assembled into self-powered enclosures. I decided that this was the most-needed function. Another bench-top unit houses a couple of digital multi-meters and a continuity tester. I use these all the time.

The “work bench improvement project” continues with various efforts to consolidate parts storage, create modules for prototyping, experimental, and demonstration purposes, and throw away redundant and trashy stuff. The current effort focuses on finishing projects that I started earlier.

A Tale of Two Towers

19 April 2015

No, it’s not another 9/11 exposé.

This is a little long-delayed article on making electronic equipment for a hobbyist workbench.

Here’s a view of my two towers:

the two towers on my workbench

Inception

I have designed and built a lot of test equipment for my hobby. I still do.

But a lot of it I end up hardly ever using, or using just once. I had a need. I built something to fill the need. It filled the need. And the need never returned. Or so it seemed.

But some needs kept coming up. A quick source of power. Need to measure a voltage. Need to measure a current, or a resistor, capacitor, sometimes even inductor. I had created a lot of different solutions for these basic needs and usually put them in some sort of horizontal enclosure. This was the standard approach. However, if I put the thing close to me so I could use it, it blocked access to the rest of the bench. And if I put it further away, I never used it, opting instead for something portable that I could put on the bench temporarily then put back somewhere else.

So one day (a year ago?…hard to say when for sure) I got the idea of trying a vertical arrangement. Maybe this was the compromise design that would keep the tools I needed the most close at hand without blocking my access to the rest of the bench.

I started on Tower One. I had a piece of plastic I was going to use for some sort of rack-mount project (19 inches wide) so I just turned it on its end and made a cabinet out of it.

tower one

Tower One

I wanted all the stuff I had put in past designs in this one. A bunch of power supplies, including a variable one. At least one meter. A selectable voltage divider and a bunch of current shunt resistors. And a signal generator. And since I was getting into Arduino, the signal generator would run on software.

I also wanted to include a “patch bay” that I could use to change cable connector types, as this was a constant problem.

And I came up with something.

It worked pretty well.

But after sitting on my bench for six months or so, it was obvious there were parts of it I hardly ever used. The minus supplies were one thing, but didn’t matter that much, as they didn’t take up that much space. The whole top section was not being used, either. The other parts were being used a good deal, but I wished I could monitor voltages and currents easier.

So I decided to build Tower Two.

tower two

Tower Two

I wanted to make this tower half the height of the other. I had a hard time finding a good enclosure, but finally decided to take the front panel of a rack-mount enclosure that I didn’t want and cut it in half. I used both halves, with a hinge between them. One half had the power supplies in it and the other half the rest of the electronics. I expanded my Arduino application to monitor 4 power supply outputs at the same time.

(I didn’t photograph the towers with the displays on because I thought they would just glare and look bad.)

I had to find a little stand to sit this on to get it up to near eye level, and settled on an old plastic speaker cabinet that was the perfect fit.

I simplified the “patch bay” to a few most essential connectors.

Result: I use the new patch bay all the time, but for some reason prefer the power supplies in the other tower. That’s probably because my current metering didn’t work out very well in the new tower.

I still use other tools quite often, including a little Radio Shack multimeter that I modified to work off an AC adapter, and a cute capacitor meter that I found online and installed in a rack-mount enclosure that sits to one side. This capacitor meter is very cool, as I often want to know cap values with more precision than they are marked – or can’t read the markings.

The Bench

This is probably the most productive bench I have ever used.

The Radio Shack temperature-controlled soldering iron is really nice, I have all my hand tools pretty well organized, and I don’t try to make it double as a table to eat at, as I used to with past workbenches in other apartments.

Yet the look of it is not yet that great, wouldn’t you agree? It still looks pretty messy.

my workbench

Part of my workbench in a unusually cleaned-up state.