Name plate and tags

Well the remote control for our transmitter is officially finished. Today as a last detail I built a couple of name tags for the cables and a bigger plate to mount on the front panel.

They are not only for aesthetic purposes but also to keep things where they should be, as sometimes they drift apart with strangers.

I cut some pieces from a scrap lamp and used the alphabet punch on them. They certainly look better with a small touch of permanent marker.

I like how they lay on the cables. All of this gives me an old time vibe feeling.

Metal name tags installed on audio and rf cables

Sunday worklog

Today I started to build the rope guides for the lightning fixture. I have some nice ground rods from a textile machine that are perfect for this.

Rope guide with rollers

On the evening I went to Futura and cleaned up a bit the stage, moving most of it to one place:

The Museum Corner at Futura

Then I started to install real cable trays instead of our improvised version with halves of water pipes. I need to cut a small section with a special bend to accommodate the opening on the wall.

Cable trays

I emptied most of the rack cabinet and installed the patchbay I built earlier. I had to drill and tap another set of holes as the power outlet interfered with the movement.

I also finished that small table:

Scope

We have this old scope for the students. It’s been unused for a while as it behaved erratically and then stopped working completely.

After setting the trigger to a more or less sane value I had something on the screen but the controls where flaky. A heavy dose of our deoxit equivalent and twisting it sprang to life. I adjusted the dc offset (drifts a bit while warming up) and matched the channel gains as much as I could and called it a day.

Fixing a Hitachi V212 oscilloscope

Sunday work log

Today I worked mostly on that remote control for our transmitter and on a simple pulse conditioner for a clock distribution system on our university.

We have a central clock reference used to synchronize experiments among various buildings. It’s not always spot on frequency but most of the time what matters is that its phase is continuous. There’s a network of underground cables that take that signal wherever is needed. Some of them are good despite their age (the youngest being around 10 years old) but others are crumbling and drowned.

On the seismograph building there’s a clock slaved to that signal and sometimes it looses track of it and lags as many as half an hour. Just as an experiment we decided to use the PPS signal out of a small uBlox GPS. A friend made a small module with the gps and an arduino to initialize it and display some ancillary status and I built a simple level shifter that makes a ~12V pulse out of that 3v logic output.

I also worked on the housing for the remote control. I’m using a weather proof junction box. After a bit of fumbling I had all the holes to mount the boards, connectors, indicators and cable glands done.

Then I finished a couple of details on the boards and hooked up everything for a trial run. The buttons and rf sense worked fine. But when I tried the dtmf audio input I got data on the digit outputs but nothing on the interrupt pin.

At first I thought that the module was bad (I accidentally fed it with 12V for a brief moment) and I swapped another with the same result.

I moved both of them on the breadboard and they worked fine. I inserted a bare wire on the socket and every time I touched GND with it I got an interrupt. But when installing the module that pin was stuck low. Which is quite odd.

I probed with the adjacent pins and all appeared open as they should. But there’s an unconnected pad on the other side, and there was a dead short to that. I used a scribing tool to clean up but the short persisted. That other pad, while not connected to anything on my board, was part of the dtmf module and when tied to the interrupt output it loaded it to the point of not being useful anymore.

When etching the board I used some fine steel wool and a strand perhaps stuck on the top side between the socket pins. After unseating the module, arduino and other connectors I charged a cap (around 3300uF) and applied it between the pair of shorted pins. Surely enough there was a spark.

And from then on everything worked as intended.

Lamp fixture: done

At least for now. The next step will be adding another support for the roof frame and rollers to guide the ropes around it to unblock the light path should we want to project from there.

Today I hanged the lower frame and then attached the cable trays with a set of bespoke clamps and self tapping screws.

Lamp fixture, metal version.

Today I started to replace that old wooden fixture with another one made of steel.

Our original plan was to install some cable trays to have a more industrial look.

Yesterday I assembled the frames on the floor:

Lamp fixture: metal frames

Today I spent most of the afternoon drilling the wood trusses on the roof and attaching the hooks. Then came the time to lower the old frame and hang the white on those hooks.

Letting it gently go down was easy:

Lamp fixture: dismantling the old one

I used some wire to attach the new frame to the old pulleys and help me lifting it near the roof. That seemed a lot easier on the planning stage but I managed to pull it off in a couple of hours.

To end this day I wound the new rope on the pulleys. Tomorrow I’ll hang the other frame (the black) and screw the trays to it.

Door handle

We have a discrete, and new, metal door but the inner handle is one that was in the house since the 1950’s.

On the outside there’s just a simple knob but it’s not linked to the lock. The handle works as intended but if we are not careful when pulling we end up with it on our hands.

I made a simple plate and kept the rod in place with an M4 screw threaded through it.

Looks like it came with the door:

Door handle

Park bench: mount

Today I worked on the base mount for that bench. I chose a 20 degree slope (taken from that guide) as I found it comfortably and it’s a round number too.

I fumbled a bit with some pipes but the cuts and copes to build it properly are more demanding than the time I had, so I settled on some channel iron. The math is a lot easier, I just needed to offset one cut by (channel width) * tan(20°) or 2.6 cm.

I’m very pleased with how I managed to make this weld around the corner in one pass:

Park bench: corner weld

DTMF Remote control and sequencer

Many years ago I built a remote control for our transmitter. It was pretty simple, just a dtmf decoder rescued from an old answering machine.

It served us well for a long time, however it was lost when we moved to a new location.

For the last couple of weeks I spent a while polishing the firmware and making new boards in KiCad. The original was very crude, just a simple on/off panel and delayed power sequence.

This one adds an RF sense and automatic restart, so if one of our amplifiers bails out on a power dropout we don’t have to do anything about it.

Yesterday I etched the boards. I ran out of toner and had to ask a friend to print the transfers. They came horrible but work fine nevertheless.

It’s amazing that nowadays buying an arduino and a preassembled dtmf decoder is cheaper than the single chips (and not counting the time to layout a more complex board).

All the design files are here: https://github.com/fm-futura/dtmf-remote-sequencer

DTMF remote

C Clamp

Just a small Sunday project.

Here at the Uni lab we have a nice articulated lamp that lacks a base. It’s been sitting on a corner for ages so I set to make a new clamp for it.

The frame is just a bit of T beam with a nut and some square tubes welded.

For the handle I used a bit of 3/8 threaded rod and a big washer I had lying around. In order to fix it I decided to make a hole along the axis and tap it to M3. After center punching the rod I screwed it to the drill press, using a center drill to align it. The plan was foiled when I tried to drill, as I left the base loose and it moved. But it’s good enough.

My initial idea was to use another nut and a locking pin behind the front washer but that used up a loot of the available space inside the clamp. After a bit of head scratching I ground a small taper and added a small washer to push the bigger one instead of a nut. I’m quite proud of how it turned out.

Homemade C clamp
Homemade C clamp

Park bench

A while ago we were given a bunch of weathered wood from a deck. Some of us have been thinking of installing seats on the sidewalk and this looked like a good opportunity.

I looked around Core77 and there’s an entry just about seating that produced this helpful guide:

I built a simple frame with square tubing and used one of the wood packs to try it out. I need to select the best planks but it’s comfy and with a bit of paint will look good.

Assorted clamps

The last two days I finished the welds on those clamps,  built some to hold the other end of the ropes and four sturdier to screw to the roof trusses. All the screws are paired with either a nylock or two nuts locked to each other.

I painted the pieces for the bottom frame with black enamel and the ones for the roof with white to match the rest of the room. I know they’ll rust in some weeks but I left the blued surface exposed. I never tire of looking at them.