The Last 10% - Metronomes

Everybody has ideas and everybody has a side project. Anyone can tell you their idea, most people can start a project, but its the smaller group who actually finish what they started. This is the group who’s work I appreciate and who I strive to be a part of. Over the course of my life I keep finding that the last 10% of a project is ALWAYS the hardest. Its that last bit of polish and love that is the most tedious. A wise man once told me that you should never talk about a project you are going to build. The mere act of talking about it is creatively rewarding enough to prevent you from starting it. I find that when thinking of projects, I focus on one key portion of the project and loose track of the big picture. Once that key component is complete, my creative mind is onto the next project. The problem is, that the original project is not finished. If you were to put an engine in a frame, sure it’s a car, but it’s not a car you want to drive in the rain and therefore not finished. Using my current project I can illustrate how much of the actual work lies outside the initial core concept.

Watch the video

When it comes to sculpture, I feel the cool happens when an object is taken completely out of context or is unable to complete the task it was originally intended. The example project is a Ticker Box. The Ticker Box, as you will soon learn, is an exercise in futility. The thing has no meaningful use.  However, in groups they seem to interact with each other and feel like they are alive.

Recently I visited a garage sale where an item caught my eye. It was a long box with six dials on the front. It looked to be some sort of power supply that could be dialed into various, accurate voltages. The thing didn’t really have any “buy me” draw until I turned one of the knobs. The knobs looked like they came from an old oven and would click into position. The tactile feel was very compelling and totally sold me. Here I am with yet another piece of useless obtanium which I have no immediate plans to use. This is where the first step to finishing what you start comes in; you can either start building something immediately, or put it on the shelf for another day. There is only one right answer here. Otherwise, you shouldn’t have bought the thing in the first place. It’s time for a new project, which is going to be based on these knobs.

In the past I have built a few micro controller based projects. Micro controllers (like the Arduino) make projects easy because your circuitry can be minimal and the behavior (where the complexity lives) is coded in software.  For this project I decided that it was time to learn something new and get more serious about analogue circuitry. Analogue circuitry is a bit more complex and less flexible than using a micro controller. Instead of being able to reprogram your item, you have to use hardware to determine behavior. The simplest integrated circuit I know about is the 555 timer chip. Having never used one I knew there was going to be a bit of a learning curve. I had lots of dials and a timer; why not have the dial control the speed of the timer? Turns out that wasn’t as easy as it sounded, which was the impetus to write this article. In theory I would end up with an adjustable timer, but no clear application for it. What is this timer going to do?

Above is a 555 timer chip and an electromechanical relay.

Ever since I started playing with electronics, I have had an affinity for old clunky electromechanical relays.  Relays are basically electronic switches, controlled by an input voltage. The adjustable timer will trigger the relay on and off. The relay isn’t connected to anything - thus, the exercise in futility. However, the relay does open and close, which creates a nice electromechanical action in response to the timer input. Now I had all the parts needed to get the project started.

The first step was to figure out how to wire up the 555 timer chip so that it put out an intermittent signal. The next step was to augment that circuit to incorporate the knobs. Turns out that the way to adjust the ticking speed of the 555 was to adjust the resistance in a portion of the circuit. I collected a bunch of resistors that had different ratings, each of which had an effect on the 555’s timing. I soldered 10 different resistors to each of the dial’s 10 positions. That was it, I was using dials to adjust the speed of a timer. Done!

Above is an image of the completed circuit on a proto board.

Above is an image of the technical parts going into each Ticker Box.

Up to this point, the project was somewhat straightforward. With 555 ticking away, it was time to make the ticks turn the relay on and off. The rabbit hole got a little deeper here, because the 555 circuitry is 12 volts DC (from a battery) and the electromechanical relay is 110 volts AC. This is where a solid state relay came in. The solid state relay is controlled by 1.2 volts, but switches a 110 volt circuit. The project got even more complicated, because the 1.2 volt control is ten times less than the 12 volts of the 555 chip. After a week of research, I found that Zener Diodes (yeah, they are real) can be used to reduce voltage. The circuit was done! Oh wait - all this was done on a proto board, so it still had to be finalized with solder.

Above is a detail shot of the custom circuit board.

Above is the completed content of a Ticker Box: power supply, custom circuit board, solid state relay, dial with resistors and the electromechanical relay.

As with everything in this project I will be doing it six times.

As you can see, wiring up the 555 and getting it to do what it’s supposed to do took a little more work than one would anticipate. I added an LED into the mix, in an effort to add some ground effects when the electromechanical relay is being triggered. Additionally, the circuit needed a power transformer. I found a wall-plug to car-socket conversion was cost effective and compact. Did I mention that I was making 6 of these things? The end game for me was to have these Ticker boxes for sale in my Etsy shop. One for each knob.  With the circuits done I thought, phew, that was a serious project. Wait a sec, what do they go in?

Above is where the 110 volt to 12 volt power is coming from. I am only using the circuitry from the inside the black casing.

Next, it was time to head to the shop and fabricate some housings for these things. I chose to make 3” by 3” by 3” steel boxes. As with most metal projects, the bulk of the work was in the metal preparation. This portion of the project was more straight forward than the circuitry part, but was more important.  They needed to be durable, and the box provided the feel for the whole project. It’s more work, but I really like using custom enclosures. If someone recognizes the enclosure you put your project in, they immediately think of Radio Shack (project boxes) or a Safeway checkout line (Altoids containers).

You cant work with rusty steel so it all has to be hit with the wire brush.

Once the metal was prepped, it was time to make tops and bottoms.

I had to machine the tops to accept the electromechanical relays and let light shine though. To each box, I added mounting points to the inside, and drilled holes for the dial and the power cord. I also made the bottoms easily removable.  Lastly, the things needed to be primed and painted. Power coating is my new favorite, but it was cost prohibitive for this project.

Prior to welding, the enclosures were clamped into place. Things tend to shift a bit as the steel cools after welding.

Above is an enclosure with its top welded on.

Each time I finished a step on the first one, I had five more to do.

Cleaned up the edges a bit.

A freshly cut rectangle in the top.

In order for LED to illuminate the plastic under the relay, there needed be a place for the light to pass through. A 1” by 1.5” rectangle does just that. I chose to use a shape wizard on the milling machine for this operation. I let the program run in the air above the box to ensure everything was going to run correctly. After that I ran the same rectangle cut program on each of the six boxes. You can see a short video of the milling on YouTube.

A finished top, with a light hole, two mounting and two holes for wiring.

Ideally the next step would have been incorporated into the previous program for the mill. Since I was mounting the same relay on each box, the bolt patterns were all the same. I wrote a simple program for the mill that moved the head above each hole to be drilled. I installed each box into the mill and started the program. The drill would stop above each hole and I would manually drill it out. This was a serious time saver and something I will be doing more in the future. I can’t count the times I have messed up a project because I missed the placement of the mounting holes.

Welded nuts that hold the bottom.

In order to service and install the electrical components, the housings needed to have removable bottoms. I welded nuts to the inside bottom walls of the housings. The four corners of each bottom panel were drilled out in order to accommodate the bolts corresponding to the nuts.  Once the welding process began it became clear that four welded nuts with bolts was overkill. Only two nuts were welded to the housing walls. The other two nuts were welded to the backside of the bottom panel.

The dials required two holes to mount; one for the dial shaft and another to prevent the dial from twisting. In addition to the two holes on the front, there needed to be a hole in the back for the power cord. This part of the project wasn’t too difficult, just time consuming. With all the holes drilled and cleaned up, all the fabrication was complete.

The bases were painted black. The sides received several coats of clear.


As this wore on, I realized that the crux of this project, or the proof of concept, was achieved ages ago.  The work went on and on after that, since the ‘productizing’ of the concept proved to be where the bulk of labor was. With the main challenge solved, I was tempted to give up at each step along the way, but that’s not my style. It was a long road but now I am done and loving these little things.



Can’t wait to see/feel one of these in action.

Posted by Paul D on Nov 09, 2011

Enter a comment - moderated

Add Comment