Friday, 19 March 2021

Sound-activated switch for a set frequency

Clap switches are an old automation gimmick from the 1980s. Basically the circuit hears a noise above a given volume (amplitude), and activates.

This project is an attempt to refine that idea, to create a switch that does the same, but responds only to a given sound (frequency).

This was inspired by watching my partner fail miserably playing South Park - The Stick of Truth.

In the game during battles, there is a timed button press during an attack that increases damage. Timing these button presses was not going well...

That noise triggers at the time the button press is required, so I started thinking about how that noise could be listened for, and the button press triggered.

Band-pass filters

This system relies on the use of a band-pass filter. There are plenty of explanations around about these and how they work, so I won't reinvent the wheel here.

For the purposes of this project, the key point is if the input has a frequency between the low and high thresholds, it is allowed through. Frequencies outside of those thresholds (bands) are rejected.

These can be built in hardware as circuits, but also in software on regular computers.

Fast-fourier Transform (FFT)

This is a well-known algorithm that, in simplistic terms, takes input over time (such as audio), and breaks it down into the frequencies it's composed of.

I'll admit, my understanding of FFTs is similar to the relationship most people have with their household appliances - know how to use it, but can't really explain how it works under the hood. There's plenty of detailed explanation for the more mathematically inclined.

So the basic concept is this

  • Pipe the audio input into the FFT
  • The FFT converts it into the frequency domain
  • Zero out all the values for the frequencies that fall outside of the range we're 'listening' for.
  • Do an inverse FFT transform, which turns the frequency domain data back into time-domain (i.e. back to real audio). This gives us sound where everything except for the range we're listening for is muted.
  • This can then be passed into a regular 'clap-switch', where we trigger if the volume of the sound is above a given level.

 

Finding the target frequency

This part of the process can be trickier than it initially seems. Sounds are composed of many frequencies, so it is necessary to select a frequency range that is unique to the target part of the audio.

To start with, I extracted the audio from the above video clip using FFMPEG, and opened it up in Audacity. This initially shows the audio waveform.


Select the area containing the sound, and select Tools, Plot Spectrum.

This will show the frequencies that exist within the selection. However, this doesn't give us all the answers. Save the plot (I just took the below screen-shot and used that). Then select another parts of the audio and repeat the exercise. Then basically it's a case of spot-the-difference, looking for a frequency spike that appears in our target audio but not the other samples.

A sample spectrum from elsewhere in the audio.
The segment containing the target sound. Circled are frequency spikes not seen in the rest of the audio,

Hardware

To run this switch I'm going to use the Next Thing Co CHIP. This is the same system I used for the TV desk project years ago. Unfortunately these are now discontinued, but there are still many ARM-based SoCs running Linux out there.

Potentially this could be distilled down further on to a smaller microcontroller, although I'd have reservations about how far you could reduce the resources until the processing time introduces enough lag to make it too slow to use.

As well as effectively being a 'proper' computer, the CHIP has general purpose IO pins, like most microcontrollers. This can provide the interface for the output of the 'clap' switch. In this case, for the sake of example I'm just hooking up a simple LED that will blink on detection of the given sound.

Although the CHIP does have microphone pins and the ability to switch it's video pin from the jack to be an audio in, for the sake of prototyping, I found it much easer to just use a cheap USB adapter which has microphone and headphone sockets.

Power comes from a standard USB phone charger.

Control is done via a serial connection to my PC, using Minicom.


Software

As the CHIP is a full-blown Linux distribution, there's lots more flexibility in the software that we use. I ended up using Java and the Apache Commons Math library.

The basic OS was pre-installed, Java 8 JDK was installed from here.

The Java code listens to the microphone input, and allows the user to load a JSON file containing details of the filter to apply - this made testing and refining the filter easier. The values are the start and end of the frequency range to listen for, and the threshold of amplitude to trigger the output (This figure can be a bit of trial and error based on how loud the input is, and can vary if the input volume varies.)

It can also be controlled via command line to either pass-through the audio to the headphones as-is, or post-filter - i.e. you hear what the 'clap' circuit would hear.

Code is on GitHub here.

Configuration

Some configuration was required to enable the GPIO pins to be activated on boot. To do this, the necessary commands (below) are wrapped in the bash script 

/etc/init.d/preparegpio.sh:

echo 1023 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio1023/direction
echo 0 > /sys/class/gpio/gpio1023/value
chown chip:chip /sys/class/gpio/gpio1023/value
 

(Refer to the CHIP docs for what exactly these mean)

This is set to run on boot by adding the below line to /etc/rc.local

sh /etc/init.d/preparegpio.sh

Finally, for the Java code to trigger blinking the LED, it triggers another SH script. I went this route as I intend to develop the Java code into a more general purpose audio tool, so didn't want to tie the code too closely to the hardware I'm using for this project.

It also has the benefit that the audio processing doesn't wait for the GPIO operation to complete, thus reducing the lag.

~/triggergpio.sh

echo 1 > /sys/class/gpio/gpio1023/value
sleep .5
echo 0 > /sys/class/gpio/gpio1023/value

Testing

While it certainly does respond to the input audio as expected, there is definitely some processing lag, as can be seen as the video progresses.

This isn't entirely unexpected, and could be overcome by throwing more computing power at the processing (The CHIP is a 1GHz processor), or possibly further optimisation of the code (or porting it to C or similar).

That might be the subject of a follow up project at a later date, but for now, this demonstrates the idea.


 



 

Monday, 21 December 2020

Slack & WhatsApp controlled Christmas Tree Lights

With the Covid-19 pandemic still dragging on, it looks like things won't be back to normal in time for Christmas.

At work there was discussion about Christmas parties, team building exercises, and other such things to try to boost morale.

I'm currently working on a project that uses WS2812 RGB LEDs (which'll no doubt wind up published here eventually), and on a whim, wondered if there existed fairy lights that use the same chip.

Turns out, there are. So obviously I had to buy some.

My Christmas tree is positioned so that is can be seen in the background when I'm on Zoom calls with work, so I thought it'd be fun if I could setup some system that would let my colleagues interact with the lights.

Once the lights arrived and I'd tested them, I got to tearing them down.

Wiring

The power supply/controller is a USB unit. I was powering it from a phone charger adapter. That also contained an infra-red receiver for the included remote. I thought about potentially working that angle, but the remote had limited options, and I wanted to offer more granular control.

From the controller to the lights was just 3 leads, which I rationalised must be +5V, Ground, and Data.

I cut the wire, figured out which was which, and connected in an Arduino. It wasn't able to provide enough current to drive the LEDs itself, to I made use of the existing charger - the charger continued to be connected to +5V and Ground, sharing the ground with the arduino's ground, and then the data line connected to the arduino.

The circuit. It works fine like this for short periods, although I later found adding a 470 Ohm resistor between arduino D12 and the first LED increased reliability over time.

 

Arduino code

I ended up using the PololuLedStrip library, and modifying the existing code for that.

Initially I'd hoped to be able to provide full RGB control, but it just seemed that the sheer amount of data being sent meant bytes were being lost, or I had to slow the data rate down to unusually slow.

Eventually I settled on using 10 preset colours, defined with numbers 0-9, being sent as a 100-character serial string - 1 character (colour) per LED. This seemed to be the best trade off of functionality and reliability.

The code can be found here.

 

The 'server'

This is a simple web server that accepts GET requests for one endpoint, and is simply there to provide a go-between for the messaging apps and the serial port.

As each LED is individually addressable, I wanted to create a format that would give users control at that level. I settled on messages with the following JSON structure

[1,"colour"]

or

[[1,2,3], "colour"]

where the numbers are the IDs of the LEDs, and the string is one of the available colours.

This would let them control either an individual LED or a series of them in an individual command.

Hooking into Slack and WhatsApp

As at work we use Slack, and we have some previous integration with it, it seemed like the obvious choice.

However, their API functionality is heavily focused on HTTP endpoints, and requires a server to interface with it. That's fine for 'proper' development, but when I'm just messing around at home, I don't really want to be dealing with opening up my home network and all that entails.

Really what I wanted was some client-side plugin functionality. There isn't an official API or interface for one, so I had to improvise.

Using the web-browser interface, and making use of Firefox's Javascript console, I added a MutationObserver to the page, and made use of the DOM to narrow in on the message elements, and get the contents of the latest message in whatever chat/channel the user was in.

The javascript for Slack can be found here.

Once retrieved, some basic checks are done to make sure that the message is in a usable format and hasn't been acted upon already, it's then passed to a local server via HTTP, where it's processed, converted to the serial format used by the arduino, and sent onward to it.

After realising how useful MutationObserver is for things like this, it was quite trivial to do the same for WhatsApp.

 The finsihed product


Thursday, 10 December 2020

Live-edge oak spotlight light fixture - part 2 - adding ambience

In my previous post, I built a hanging light fitting of live-edge oak and recessed GU10 spotlights.

There is actually more to the project.

Sometimes, spotlights can be a bit overpowering, and it's preferable to have some ambient, indirect light.

During construction, I had the idea of creating this light in a way that would allow use of the spotlights, an ambient light, or both.

To create the ambient light, I used LED strips on the reverse (upward-facing) side, to reflect light off the ceiling.

I cut some thin strips of oak with a 45-degree angle and mounted them in a rectangle on the back - angled side outward, to help direct the light. An RGB LED strip was mounted all around this.

Control

I initially thought of using the LED driver that tends to come standard with rolls of LED strip, but as the existing wiring leads to only one switch, without some rewiring through the ceilings/walls, it would be limited to either having both the spotlights and the ambient light on, or just the spotlights on without the ambient light - it would not be possible to have the ambient light on without the spotlights.

In order to combat this, and to lay groundwork for a potential future project, I included a solid-state relay and an Arduino. The arduino would drive TIP31 transistors to drive the 3 channels for the LEDs red, green and blue, and additionally control a solid state relay which would act as the switch for the spotlights.

The idea would then be that the light switch would remain on, more like a utility switch, and then all control of the light fitting would be handed over to the Arduino.

 

Power

 

The original wiring sketch.
it's just a rough sketch,
not a proper wiring diagram.
 
The LED strips take 12V, and the microcontroller takes 5V, so a PSU is needed to bring the power down to usable levels.

For this I used an old net-book power supply. This was wired into the back of the light fitting. Caution is needed to make sure that nothing too powerful is used, as typically a houses' lighting circuit breaker is tripped at a much lower current than the mains sockets.

 

Revised to include the additional components
This would normally be plugged into a wall socket, where it's plug would have a fuse. However in order to wire this into the lighting wiring, the plug would need to be removed - obviously this introduces a safety concern. To ensure that this would still be fused, I replaced the wall switch for the light to one that includes a fuse, ensuring that the light is behind the fuse.

 

Communication

To communicate with the Arduino, I used a cheap HC-05 bluetooth to serial adapter, the same as I've used in other projects like the Bluetooth Macro keyboard app.

The arduino receives 4 bytes, followed by newline characters. These correspond to 1 byte each for the red, green and blue channels in the LED strip, and the final byte is either a simple 0 or 1 to indicate if the spotlights should be on.

For now this is sent by pairing with my phone and using a bluetooth serial terminal app from the Google play store. I'll probably create a more custom app in future, but for proving the concept, this works just fine.

 

Saturday, 28 November 2020

Live-edge oak spotlight light fixture

The basic idea

The idea is that the fitting uses GU10 spotlight fittings like those typically recessed into ceilings.

However, instead of recessing them into the ceiling, they're recessed into a piece of live-edge wood, which is hung from the ceiling like a more traditional light fitting.

The woodwork

There's not much really in the way of woodwork in this project, just clean off bark and splintery bits from the live edge, preserving as much of the edge as possible.

Quite a bit of sanding was also needed to clear up the surfaces.

The end of the board I had was cleanly sawn which I thought detracted from the live edges, so I broke the corners down with a carving disc on an angle grinder.

Creating grooves for
the spotlights latches
Then measure the centre line. I started by taking the average width of the board and working from that, but there is some leeway - having both sides be live edge makes this near impossible to find a perfect centre line, but ultimately as long as it looks central to the naked eye.

The spotlight fittings are not designed to go through the thickness of the board - after all, they're intended for plasterboard ceilings. While it won't affect the functioning of the light, it means that the spring loaded clips that latch. To work around this, I used a forstner drill to thin around the edge of the spotlight holes where the latch would sit - This is easier to do before the main spotlight hole is cut out, to stop the forstner bit from slipping.

Then I cut out the holes for the spotlights by drilling a pilot hole and widening with a jigsaw.

Test fit of one of the light surrounds

Wiring the spotlights

The three spotlights are wired in parallel, split across 2 junction boxes. Having them in parallel means that if one bulb was to fail, the others could continue to function.

 

To make installing the light easier, the lead that connects from the ceiling to the wood itself included a 'kettle plug' style plug and socket, simply so that the wiring could be done on the workbench, and just plugged in at the time of installation.

 

Mounting

The ceiling roses were purchased, and have simple hooks on them for hanging the chain.

Eyelet screws were attached in the back of the wood at each corner, from which the chain was attached.

Enough leeway was given on the chains so that adjustment could be made to ensure that the light hangs flat.


Friday, 23 October 2020

Combination pinboard and cinema poster frame

Even before Covid-19, people were already starting to talk about "work-life balance", and it's effect on health.

When Covid made working from home the norm, maintaining that balance became even harder, especially for those whose homes are more open-plan, meaning the same rooms they go to relax could end up also being where they go to work.

This project is aimed at exactly this problem.

During the day, the frame can be opened up, to reveal a pin-board where all the usual work notes and paperwork can be pinned, but once the working day is done, the frame can slide closed, shutting the metaphorical door on office life, leaving just the poster visible, more in fitting with a relaxed home lounge look.

The 'front' (poster) frame

This frame is more akin to a traditional frame, but as it will be the sliding component, and so not directly mounted to the wall, keeping the weight low is important.

As with the back frame, the joints are mitred half-lap. The same oak is used, but much thinner (roughly half inch). A rebate is cut in to seat the glass, poster and backing board.

With weight limitation in mind, thin perspex was used in place of glass. The rest of the frame is pretty standard - a sandwich of the perspex, the poster, backing card, and then hardboard (in this case, up-cycled panels from a hollow core door) all held in place with some pins.

The 'back' (pinboard) frame

To start with, this is a standard mitred half-lap jointed frame, albeit deeper than a normal frame - about an inch. It also does not have any rebate or groove, as it's not needed.

The pin board that I'm re-purposing is another of the same style I used for the desk organiser. It's smaller than the poster frame, but this is by design to allow room for the sliding mechanism.

The two long sides are removed.

These are replaced with longer oak sides that attach it to the frame. On one side this is simply screwed into the larger frame, and on the other, small grooves are cut into the frame for it to fit into, similar to a tenon.

 

This second side leaves approximately 4 inches between the edge of that inner frame, and the edge of the main frame.

 

The rail mechanism

2 4x2" pieces of oak are drilled with a 20mm hole lengthways, and then glued in place at the top and bottom of the frame, filling this gap.

Then, the entire frame is cut lengthways, halfway through these pieces of oak, leaving 2" of it on either side. These will form the rails.

The 20mm hole is extended through the 'long side' part of the inner frame, at both ends.

The 'thin' part of the frame - the one without the pin board attached, is the part of the back frame that the front frame will mount to, and be the part that slides out.

16mm aluminium tubing was inserted through each of the channels. On the thin side of the frame, a screw was driven perpendicular to the 20mm hole, fixing the tube in place and adding some support to the glued in block.

These two tubes are then threaded through the 'fat' part of the frame.


Joining the two frames

Screws from the back frame are driven through into the front frame on the left hand side (the 'thin' side).

To prevent sagging when the frame is opened, leather loops are attached around the other end of the tubing and screwed into the back of the front frame.

This makes the sliding part of the frame counterbalance it's own weight.

The whole thing was finished with a coat of danish oil, 4 angle brackets were added and it was mounted to the wall.

 

 

Friday, 11 September 2020

Boosting broadband speed with satellite co-axial cable

When I moved into this house, there was a lot of extraneous wiring. Phone line extensions that went nowhere, that kinda thing, so I ripped out everything back to the master socket by the front door.

When fibre was enabled, I had a visit from an Openreach engineer, reporting a fault detected on the line - the case was the old master socket had some corrosion, so he replaced it with a new one.

However, I want to move all my network gear to the under-stairs cupboard, and branch everything from there. As I don't use a landline, this would mostly just mean Wi-fi and a few ethernet cables.

There's a not insignificant cost to have Openreach come out and move the master socket, so I'd rather avoid that. It's also not something you can really do yourself - the master socket marks the point in the connection where the providers responsibility for the wiring ends and yours begins. If you tried to move it yourself and screwed up, there's a significant charge to that too.

Just using a phone extension lead works, but slows the broadband speed noticably.

Unfortunately, due to the age of the phone system and it's various evolutions over the years, finding decent, up to date information is not as easy as it should be.
I manged to put together a DIY solution that boosted my broadband speed by approx 50% (~14 Mb download speed with regular phone extension, to ~21 Mb using my solution)

This was done by combining a few other ideas and sources of information.
This is what worked for me. Your results may vary, and usual "don't try this at home" warnings apply.

Moving the master socket without moving it

I found this guide which shows a master socket with 'A' and 'B' connections, which it states, you can run to another socket using CAT5 network cable, which will have a similar effect to moving the master socket, as it bypasses a lot of the filtering of the sockets, and CAT5, being twisted-pair cable, has better shielding qualities than regular phone extension.

But unfortunately, my master socket is the newer type 'NTE5C' socket, so it doesn't have the same connections.. It does have a similar A and B connector, but it's on the provider side of the socket, and is in use, so I don't want to mess around with that.

It give me an idea though. Even if that route is out of the question, a lot of the interference comes from the cabling used. If I were to create a phone extension lead from CAT5, it should still be an improvement to a regular phone line. 

Looking up how to install a telephone extension on the NTE5C type of master socket led me to this video which shows using the front panel to connect an extension using pins 2, 3, and 5.


Pins 2 and 5, according to the first article, are the equivalents of A & B.

So, what if I put in a telephone extension using that connector like in the video, but instead used better cable as per the article? In theory, the speed should improve due to the increase in cable quality, but would lose a bit because a microfilter would be required (because it's not been pre-filtered.)

I also thought, if CAT5 beats regular phone cable because it's twisted pair gives it some shielding, then wouldn't something more shielded so even better? I had a usable length of co-axial cable, the type used by satellite dishes and antennas.

This is a single copper core with a mesh-like shield all the way around it. These would provide the connections to pins 2 & 5 (I used the core for pin 2, the shield for 5, but I don't think it'd matter which way round).

The article does recommend solid core wire, which the core of the coaxial is, but the shielding is not, so I guess there may be some performance trade off there.

This was wired to a regular phone socket under the stairs, in which there's a microfilter and the router.

Initially the speed fluctuated a bit, but once it bedded in, it settled on a speed (as reported by the router) of approximately 21Mb, which is up from the approximately 14Mb that was achieved with the same length of regular phone extension cable.

I'd be tempted to experiment further (ideally with something with twin solid cores and shielded.), as there's still a bit of room for improvement - at the master socket directly, the router could get 26Mb - but for now it's fast enough.


Friday, 21 August 2020

Straight razor from table saw blade

So a while back I replaced the table saw blade in the workshop and got the idea in my head to try and make a straight razor out of it.

I sketched out a quick design and then cut it from some scraps of redwood (the same stuff I used in the ring box project - not sure if that's the correct species, but it's wood, and it's a red-ish colour, so close enough.) on the bandsaw. Fortunately I had two scraps the same thickness, so I needn't worry about the thickness of each of the scales (sides) being identical.

The blade itself was sketched out in marker on the old table saw blade and cut out with an angle grinder. Once the rough shape was done, a mix of bench grinder and rotary grinding tools were used to refine the shape.

The gap between the 2 scales of the handle was padded out using some brass sheet, cut to match the shape of the scales, whilst including cut out space both for the blade to fold in to, and to allow the tang to rotate into when the blade is opened.

This, and the scales were both epoxied together, and then two holes were drilled and brass pins added, for additional strength and their own aesthetic quality.

The third brass pin provides the hinge that the blade will pivot from to make the opening and closing mechanism.

Before the blade and handle were put together, it was easier to finish each part separately.

In the case of the handle, this meant sanding to round off the edges and make it more comfortable to hold, and a wipe out with danish oil.

In the case of the blade this meant a lot of grinding, sharpening and honing to get it to a sharp enough edge to cut hairs. With hindsight although it probably isn't the best steel to use for a blade, it is sharp enough to shave with - it just requires frequent honing.

But, at the end of the day it works, I'm pleased with how it's turned out, and I learnt a bit more about blade making and the dark arts of sharpening and honing along the way. I also now totally get why some people fall into this particular niche rather than just more general metalworking... I'm actually quite tempted to go find some better steel and make another already.