Hey, so its been a while, there’s been a few projects since the last post, but I haven’t written them up 🙄 .
In an effort to stop the projects accumulating in the half-finished pile, I made an effort to take this project that has been sitting on the workbench for ages and put it on display. Its simple enough but I’m pleased with the result.
Ages ago I wrote some code for an HTU21D temperature and humidity sensor. I made an outdoor housing for the sensor and all, and used it for a while, but the display was a bit impractical. Anyway, this time I used a 2 line 20 character VFD (vacuum fluorescent display) I’ve had for years (sitting in the bits and pieces pile) to display the sensor measurements. I’ve always liked the display and now its time to show it off.
So, this post is more about the making of the display. I used some clear acrylic sheet and a bunch of fasteners and standoffs I’ve collected over the years. I learnt a few things along the way mainly around working with acrylic. Also, it was a chance to learn to use brass threaded inserts which I bought to use with some 3D printing projects, but I haven’t used them yet. Maybe there’s something useful in here for you.
I began with a layout of the components – the VFD, arduino and the HTU21D – that would fit on my small sheet of acrylic. I made this layout using Onshape (its a 3D modelling program, but I used it create a scale 2D drawing of the layout.) then printed it out and glued it to the acrylic to use it as a template.
I used a multitool to cut the two halves of the acrylic out. Probably not the best tool for cutting acrylic because the acrylic tends to melt and gum up the blade. (personally, I think multi-tools are very over hyped and suited for very specific/dedicated jobs such as plunge cuts in tight, awkward places. As for being a “jack of all trades” tool, they definitely are not that kind of tool and the noise they make is horrific.) Anyway, I used a multitool because I don’t have a bandsaw and I didn’t want to use a hacksaw. I reckon a hacksaw would have been faster in retrospect. (Top tip, power tools don’t necessarily have to be the first tool of choice).
To make the radii on the corners I just used a file and its very easy to make a nice finish when you have a guideline to follow.
Once cut to size, I drilled out the holes for the screws and threaded inserts. A big tip when drilling acrylic or other plastics or brass, make sure your drill bits’ cutting edge is dull. I learnt this tip from AvE or Jimmy Diresta or someone else and its an excellent tip. The dulled drill bits don’t bite into the plastic and cause it to catch or shatter the piece. I bought a cheap set of drills and dulled all the bits they are now dedicated for use with plastic and brass. I don’t have a lot of experience working with sheet plastic so I experiemented with different drill speeds – I can’t remember if I had any major revelations, but I found that all my holes chipped when the drill exited. This chipping may be due to excessive pressure on the drill bit as it cut through.
A lot of the screws had to be cut to size because they were too long – just used a hacksaw for this. Once cut, a file was used to remove the burr, and then run through a die to fix up the threads for some of the fasteners. The threaded inserts are going to mate with the standoffs on the back piece of acrylic. I had to put short lengths of thread into the standoffs and I used threadsealant in place of threadlocker to do this.
Inserting the threaded inserts into the acrylic was a challenge. I used a soldering iron to press them into place. However, a lot of the times the threaded insert got stuck to the tapered soldering iron tip when I was pressing it down and when I went to lift the iron, the insert pulled out of the plastic. I think a dedicated soldering iron tip that isn’t tapered would be more appropriate. Also, I drilled the hole diameters out a bit too big. I drilled the holes to be the same diameter as the collar/shank of the insert but I think that that was still too big. Next time I will further undersize the drill holes.
Once all the mechanical parts were made, everything was assembled. Some of the holes didn’t quite line up – this is because the threaded insert didn’t go in completely square and the standoff is at a slight angle. However, I was pleased with how it began to come together. Top tip, buy Allen Keys with ball-ends, they are so useful.
Once all the wiring was completed and software was loaded, it was time to hang it on the wall.