Author Archives: Brian Benchoff

BOM Cost Optimization and Tindie Badge Engineering

via hardware – Hackaday

For the last few months, I’ve been up to my neck in electronic conference badges. This year, I created the single most desirable badge at DEF CON. I also built a few Tindie badges, and right now I’m working on the logistics behind the Hackaday SuperConference badge. Sit tight on that last one — we’re doing something really, really special next month.

Most badge projects are one-off production runs. This is to be expected from a piece of hardware that’s only meant to be distributed at a single event. The Tindie badge is different. It’s now a thing, and we’re building multiple badges for all the cons and conferences Hackaday and Tindie are attending for the rest of the year. This means I have the opportunity to do hardware revisions on the Tindie badge. Right now I’ve built three versions of the Tindie and we’ve distributed about two thousand of these kits at DEF CON, Maker Faire New York, and the Open Hardware Summit.

After about two thousand units, I think we finally have this down. This is how I designed three versions of hardware in as many months and cut the BOM cost of each badge in half. This is bordering on a marginally impressive piece of engineering, and a great lesson on BOM cost optimization.

The Tindie Badge, Mk. 1

This is the first revision of the Tindie badge. I wrote about it on the Hackaday blog earlier, but the simple version is pretty much Jasmine saying, “Hey, we should build a Tindie badge for DEF CON”. It’s not like I didn’t have my hands full at the time, so I agreed to take on the project. We designed, ordered, received, kitted, and distributed three hundred Tindie badges in two weeks.

The Mk. 1 Tindie badge is just about as simple as it gets. There’s a battery holder, a battery, and two flashing RGB LEDs. Some BMP hacking in Eagle makes for a great PCB, and a ‘pin clasp’ soldered to the back of the PCB makes it a true wearable.

Kitting and distribution of this badge went great, and the BOM cost was reasonable: $1.83 per badge at quantity 300. Great for DEF CON, and a potential to be a *great* bit of swag. A lot easier to lug around than a bunch of t-shirts, in any event.

The Tindie Badge Mk. 2

With the success of the Tindie DEF CON badge, we decided to make a few more up for our next event: World Maker Faire in NYC. Confident in our ability to put together badges quickly, our target quantity was 1,000. A thousand badges, and only a month and a half to get it together. Not a problem.

The changes from the Mk. 1 to Mk. 2 badge were purely cosmetic. While using layers of copper, silk, copper resist, and mask work well enough as an artistic board, I wasn’t quite happy with how the first version of the Tindie badge turned out. There wasn’t a whole lot of difference between the dark blue and light blue, the eyes could have used more definition, and Tindie’s rivets should look like actual rivets. This meant I needed to change some of the dark areas to tinned areas. Not a problem — it’s just playing around with Illustrator, BMPs, and Eagle.

The Mk. 2 badge for Maker Faire was a success, both as a bit of swag and from an engineering standpoint. Instead of the $1.83 the first version cost, the Mk. 2 version was only $1.23. We used the same suppliers for the parts, so really that’s just a quantity discount. This is still a significant cost reduction, and considering how many stickers we give away at events, this is a very attractive bit of swag.

Was I happy with it? No. The plan to put tinned copper everywhere didn’t pan out, and the original badge looked better. At the very least, the nose and ears should be dark blue. There’s only so much you can mock-up in Illustrator without having a finished board in your hands. Still, we made 1,000 for Maker Faire, and the cost per badge came way, way down.

The Tindie Badge Mk. 3

Our next event after Maker Faire was the Open Hardware Summit in Denver. After that, it’s the Hackaday Supercon where we’re expected to make it rain robotic dog heads.

The most important issue to fix was, of course, the art. The basic idea behind the art was to refine the design, make the nose and ‘inside’ ear dark blue, keep the rivets silver, and use the white silk a bit more. I wrote another Hackaday post on how to do this art in Eagle, and that went together pretty easily. We’re all happy with the results.

The Mk. 3 Tindie Badge is a major revision. We’re doing actual, real, hardware changes. What’s the biggest change? A switch. I’ve tested the Tindie badge, and a fresh battery will blink the eyes for days, but some people like to take the battery out for some reason. Whatever, we need a switch.

Tindie Badge Mk. 3, with the handy-dandy switch

The requirements for this switch meant it had to be an SMD (so the front art wouldn’t be messed up) SPST switch. Smaller was better, and as with all the components, we’re looking for the cheapest option. We landed on an Alps switch from Mouser, available for $0.14 in quantity 1000. That’s cheap enough.

With board art we’re happy with and the BOM pretty much sorted, let’s do a cost breakdown for 1000 Mk. 3 badges:

Part Unit cost Total Cost Source
Bags $0.03 44.96 AliExpress
Tacks $0.11 114.11 AliExpress
Battery holder $0.36 357.26 Digikey BK-916-CT-ND
Battery $0.17 170.35 Amazon
5mm LED $0.02 49.80 Amazon
Boards $0.54 321.77 Seeed
Switch $0.14 144.00 Mouser 688-SSSS810701

The total cost per badge, in quantity 1000, is $1.37, basically the same as the Mk. 2 badge, but adding a switch. Acceptable, but I’m still not happy with how much we’re paying for battery holders and switches. We’re going to roll with the Mk. 3 badge for Open Hardware Summit and Supercon, but I’m going to make a few changes to the BOM going forward.

Real engineering and BOM cost optimization

We’re not going to cut the BOM cost on the bags, tacks, or the LEDs. Those are already as cheap as they’re going to be. Likewise, the price of the PCB isn’t going to come down much unless we order more in obscene quantities.  I shopped around for batteries before building the first one, and trust me, Amazon has really, really cheap CR1220 cells.

This basically leaves the switch and battery holder as the places where we’re going to cut costs.

Two nearly identical switches. The switch on the left costs $0.14 in quantity 1000, the switch on the right costs $0.03 in quantity 1000

The first switch I found that fit the bill was from Alps, but quite a lot of electromechanical parts have a Chinese equivalent that’s more or less the same. After a bit of searching, I found this guy on AliExpress. Take a look at the drawings of both: No, they’re not identical. The ‘studs’ on the bottom of the switch are different; the AliExpress switch has 0.7 mm diameter studs, the Alps has 0.8 mm diameter studs. If you really study these drawings, they’re more or less the same. They’re effectively interchangeable, and if you make a part for one in Eagle, you have a part for both.

Here’s the kicker: I can get 1,000 Alps switches for $144. I could also get 1,000 of the AliExpress specials for $31.26. That’s $0.14 a badge for the Alps version, or $0.03 for the AliExpress version. I just saved eleven cents. For 1,000 boards, that’s a hundred and ten bucks. Awesome.

The biggest expense on the BOM is the board, and there’s little I can do to change that. The next biggest expense — by a large margin — is the battery holder. Not the battery, mind you: the battery holder. This is just a tiny piece of stamped metal, and it costs $0.36 in quantity 1,000. Unfortunately, AliExpress doesn’t help me here. The vast majority of CR1220 battery holders from the usual Chinese suppliers are plastic, through-hole components. I don’t want that; they’re bigger parts, they’ll ruin the art on the front, and they’re still pretty expensive at about $0.20 in quantity 1,000.

The battery holders for the Mk. 1, Mk. 2 and Mk. 3 badge were from Digikey. They work, they’re great, but you should always do a search on both Mouser and Digikey before designing something. (Or sign up for Findchips. That would have probably saved some money.) Here’s what I found on Mouser. It’s a different part from a different supplier, and it’s only for CR1216 and CR1225 batteries — not CR1220 batteries.

Those of you who know how the names of coin cells are derived are laughing right now, but here’s what’s going on. The first two numbers are the diameter. These batteries are 12 mm in diameter. The second two numbers are the thickness. A CR1216 battery is 12 mm in diameter and 1.6 mm thick. A CR1225 battery is 12 mm in diameter and 2.5 mm thick. Of course my CR1220 battery will work in a battery holder that accepts both 1216 and 1225 batteries. Why the Mouser part wasn’t labeled as being a CR1220 battery holder is beyond me.

The Mouser part is $0.19 in quantity 1,000, saving me $0.17 per board. That’s $170 in quantity 1,000. Let’s look at that BOM again, with the new parts:

Part Unit cost Total Cost Source
Bags $0.03 44.96 AliExpress
Tacks $0.11 114.11 AliExpress
Battery holder $0.19 191 Mouser 712-BAT-HLD-012-SMT
Battery $0.17 83.35 Amazon
5mm LED $0.02 49.8 Amazon
Boards $0.54 321.77 Seeed
Switch $0.03 31.26 AliExpress
Total Cost: $1.09

After three revisions, we’re happy with the art on our Tindie badge, and we brought the cost down and saved almost a dollar per badge. That’s really incredible, and a testament to how much you can save just by seeing what options you have available to you.

Don’t call them Diamond Dogs. That’s the wrong album.

You’ll catch your death in the fog

What are the plans for the Tindie badge going forward? We’ve pretty much got the Supercon order lined up, and that’ll be the last con we’re going to this year. Next year, though, we’re distributing Tindie blinky badges far and wide.

The Tindie badges are some of the cheapest swag we have, and people love them. It’s a soldering kit, which fits in well with the whole, ‘make and sell hardware on Tindie’ thing we’re going for. These soldering kits are also much cheaper and much more easy to distribute than t-shirts. We’re aiming for several thousand by New Years, and we’re going to make it rain robotic dog heads.

This badge was an experiment. At the time I ordered 300 boards for the Mk. 1 Tindie badge, I had no idea how it would turn out. If we were doing these boards through OSHPark, it wouldn’t be a problem; [Andrew Sowa] already figured out how the purple PCB stackup looks when split into individual layers. Blue soldermask, though, is a bit trickier and demands experimentation. You can make reasonable guesses on how it will look in Photoshop, but it’s never quite right. I’m still not happy with the results, but some of my other pursuits are focusing on truly custom color PCBs and multicolor PCBs. Eventually, I’ll get something that looks fantastic.

Going forward, there are a few options for what we can do with the Tindie badge. I’m doing a few experiments with custom silk and solder mask, and I think this is the perfect platform to demonstrate a few new techniques. The top of the list for these experiments is an  Aladdin Sane Tindie badge, a Kiss Army Tindie, and maybe one with the Mike Tyson face tattoo. Or Chakotay. I always get those mixed up. Look forward to multicolor Tindies sometime around March next year. That’s when the 2018 conference season starts up, and we’ll be distributing these things far and wide.

Filed under: Hackaday Columns, hardware

Inside This Year’s Queercon Badge

via hardware – Hackaday

At this point, it’s not really correct to describe DEF CON as a single, gigantic conference for security, tech, and other ‘hacky’ activities. DEF CON is more of a collection of groups hosting villages, get-togethers, meetups, and parties where like-minded individuals share their time, company, electronic war stories, and whiskey. One of the largest groups measured by the number of rideable, inflatable unicorns is Queercon, a ‘conference within a conference’ dedicated to LGBT causes, a rager of a party, and a killer conference badge.

The Queercon badge is always a work of art, and this year is no exception. Last year, we took a look at an immaculate squid/cuttlefish badge, and a few years before that, the Queercon badge was a beautiful 3.5″ floppy embedded with far too many RGB LEDs. This year’s Queercon badge was equally as amazing, quite literally pushing badgecraft into another dimension. The folks behind the Queercon badge just wrote up their postmortem on the badge, and it’s an excellent example of how to push PCBs into the space of human interaction.

The development of the 2017 Queercon badge had a really tough act to follow. Last year’s Blooper squid/cuttlefish badge is a high point in the world of functional PCB art, and by January of this year, the team didn’t know where to take badgecraft next.

In the end, the QC badge team decided on a ‘failsafe’ design — it wasn’t necessarily going to be the best idea, but the design would minimize risk and development time.

A single 2017 Queercon badge

The two obvious features of this badge are an incredible number of tiny RGB LEDs, and very strange hermaphroditic edge connectors, allowing these badges to be plugged together into a panel of badges or a cube. What does this badge do? It blinks. If you have five friends, you can make something that looks like the Companion Cube from Portal.


The killer feature for this badge is a vast array of RGB LEDs. Instead of going with WS2812s or APA101s, the Queercon badge team found simple, 0604 RGB LEDs, priced at about $0.026 a piece. There are 73 LEDs in total, all driven by the same TI LED driver used in previous years, combined with two shift registers and 15 FETs to control the LED commons. Although the LED driver is able to address all 219, and even though the badge is powered by a 32-bit ARM Cortex M3 microcontroller, this is pretty much the limit of how many LEDs can be controlled with this setup.

The Queercon badge always has a bit of interconnectedness built in, and this year is no exception. This year the badge uses a strange universal connector mounted along the four sides of the badge. When one badge is plugged into the other, they mate producing a ‘fabric’ of glowing badges. The range of motion on this connector allows for 180 degrees of rotation, but surprisingly most Queercon badge holders only assembled single planes of badges. It took a bit of cajoling from the badgemakers to get people to assemble a cube, and no other weird shapes were constructed out of multiple badges. If anyone likes this idea of interconnected badges, I would like to personally suggest equilateral triangles — this would allow for icosahedrons or hexagon-based solids.

A Game

A badge wouldn’t be complete without a game, and the Queercon badge has it in spades. The UI/UX/graphics designer [Jonathan] came up with a game loosely based on a game called ‘Alchemy’. Every badge comes loaded with a set of basic elements (air, fire, water, earth), represented as pixel art on the 7×7 RGB LED matrix. Combining these elements leads to even more elements — water plus fire equals beer, for example. Think of it as crafting in Minecraft, but with badges.

Starbucks was responsible for sponsoring a portion of Queercon this year, so ten special badges were loaded up with a fifth element: coffee. Elements derived from the coffee element required a Starbucks sponsor badge.

As we all expect from a DEF CON badge, there was a crypto challenge and contest. The full write up is available here, with the solution somewhat related to a cube of badges.

A Complete Success

When the badges came back from the fab house, the failure rate for this year’s Queercon badge was 0.7%. That’s an amazing yield for any independent hardware badge, and is honestly one of the most impressive aspects of this year’s Queercon. Failure modes during the con were probably related to spilling a drink on a badge, although there was a rash of failed CPUs. This is probably related to ESD, and during the con rework of failed badges was basically impossible because of drunk soldering in a dimly lit hotel room.

If there’s one failure of this year’s Queercon, it’s simply that it’s becoming too popular. From last year, Queercon saw 200% growth for the main party, which meant not everyone got a badge. That’s unfortunate, but plans are in the works for more inventory next year, providing DEF CON 26 isn’t cancelled, which it is. A shame, really.

Filed under: cons, hardware

Pogo Pin Serial Adapter Thing

via hardware – Hackaday

A few weeks ago, I was working on a small project of mine, and I faced a rather large problem. I had to program nearly five hundred badges in a week. I needed a small programming adapter that would allow me to stab a few pads on a badge with six pogo pins, press a button, and move onto the next badge.

While not true for all things in life, sometimes you need to trade quality for expediency. This is how I built a terrible but completely functional USB to serial adapter to program hundreds of badges in just a few hours.

This is not the right way to do this.

As is usually the case for any tutorial I write, this is not the right way to do things. In commercial or manufacturing settings, pogo pins are usually found in test or programming jigs. In these jigs, the pogo pin is mounted perpendicular to a PCB, with each pin running through a second identical PCB mounted on standoffs. Just look at these fantastic products on Tindie for an example. These two PCBs provide mechanical stability and electrical connections to each pogo pin. This is a very robust system, but building one of these test jigs means I need to order a few PCBs. I didn’t have the time to do this, so I needed another solution.

Three minutes in Eagle, and it will work.

All I need is some way to hold six pogo pins on 0.1″ centers, with a few pads to wire these pins up to a USB to serial adapter. A single PCB to do this is extremely simple — all you need are a few pads to hold the pogo pins and a set of holes to plug a serial adapter into.

I managed to whip up a PCB (right) for this in about three minutes. It’s extremely simple, with the only remarkable feature being six very long pads for the pogo pins. If you’re very good at applying solder paste by hand, the surface tension of melted solder will align the pogo pins, leaving you with six perfect pogo pins all aligned and parallel to each other.

A poorly assembled Adafruit Fiddy. You have no idea how annoying these misaligned pins are

A PCB solution is easy, but it also takes time. Unless you have a PCB mill sitting in your lab, you’ll have to make due with ordering this board from OSH Park or something. Sometimes you need a pogo pin programmer right now.

If you don’t have a PCB mill, I hope you have a 3D printer. Last year, [Timothy Reese] created the Fiddy for Adafruit. This is a 3D printed ‘clip’ for six pogo pins, designed to clip onto the end of an Adafruit Pro Trinket for FTDI programming. Before designing my own pogo pin adapter, I made Fiddy. It performs its job well. The Adafruit Fiddy will clamp down on small boards, and it will program them.

There are a few shortcomings to the Adafruit Fiddy. I found my 3D printed version to be a little too flexible, although this is probably because I printed it in ABS, not PLA. The Fiddy is a little bulky. I also don’t need a programmer that clamps down on a board — I’m more than happy to hold a serial programmer against a board for forty-five seconds if it means the pins are a little more secure and the device is a little more robust.

Here’s what I did

There’s the lit review for the existing solutions for a simple, handheld pogo pin programmer. They’re all good, but I needed something right away. Except for the pogo pins (available wherever fine electronics are sold), I only needed a few items that were already on my workbench:

  • 30 AWG Kynar wire
  • 5-minute epoxy
  • Solder
  • Any random “FTDI” USB to serial converter

For this project, the pogo pins will be held in place with a 3D printed adapter. After a few minutes in OpenSCAD, I came up with this model. It aligns six pogo pins on 0.1″ centers, and can be epoxied to the back of a standard, off-the-shelf USB to Serial adapter.

module pins(){
  for (a=[2.54:2.54:15.24]){
    cylinder(d=1.45,h=21, $fs=0.01);

module front(){

module back(){




There’s not much to this 3D printed pogo pin adapter. Think of these 3D printed parts as more of a jig, with a small amount of epoxy providing the mechanical strength.

These parts were printed at a very low layer height (0.05mm) using whatever filament was already in my printer. The orientation of the parts on the bed required support for the overhangs that would become the space behind the normal FTDI pin headers, and a passthrough for the Kynar wire from the pins to the pads.

In normal applications of pogo pins, you’d simply place the pin in a circular pad and solder the brass casing to a PCB. I don’t have this option, so I need to attach Kynar wire. I did this by stripping the Kynar, placing 2-3 millimeters of stripped wire in the hole at the non-pogo end of the pin, tacking it down, and wrapping the rest of the stripped wire around the pin. A tiny bit of solder holds everything together, and a small bit of heat shrink will keep the pins from shorting to each other once this is assembled.

After preparing six pogo pins, I had to sandwich all of them between two pieces of plastic. If I have one tip on how to do this, it’s, ‘go slow’. I used five-minute epoxy for this, installing one pin at a time and making sure they were all aligned and even. It takes patience, but it will work.

After that, the only thing left to do was to solder the other end of the Kynar wire to the FTDI adapter. It’s small, fiddly soldering, but it can be done.

Did it work? Yes. Is it good? Ehhhh….

While I was able to program a few hundred badges with this pogo pin serial adapter, I’m not going to call this a ‘good’ solution. There are a few issues with this device, and I’m actually surprised it worked in the first place.

After programming, the ESP8266 on the badge restarts, and the LEDs turn on. While the power supply for the FTDI adapter is capable of providing the required ~300mA to the badge, I should have used a larger gauge wire to attach the pogo pins to the USB to serial adapter. This really isn’t a big issue, but it is an issue.

Additionally, I had to be very, very careful not to get any epoxy on the ‘springy’ part of the pogo pins. It’s easy to not screw up the springiness of pogo pins if you’re dealing with solder, but epoxy gets everywhere. I found that a quick rub down with isopropyl alcohol does clean the pins, but this is still something I wish I didn’t have to deal with.

If I had to do this again, with no limitations on time or money, I would take the PCB I created in Eagle above, grab an FTDI chip and a USB connector, and simply build my own USB to serial adapter that uses pogo pins instead of pin headers. This actually wouldn’t be that much work — two hours to design the circuit, maybe an hour assembling it, and if everything goes right I’d have the perfect tool for the job.

However, sometimes you just have to solder and glue some crap together and hope it works. That’s what I managed to do here, and yes, it did work.

Filed under: Featured, hardware, Skills

Let’s Play Spot The Fake MOSFET

via hardware – Hackaday

Recently, the voice push to talk circuit in [Ryan]’s BITX40 radio was keyed down for a very long time. Blue smoke was released, a MOSFET was burnt out, and [Ryan] needed a new IRF510 N-channel MOSFET. Not a problem; this is a $1 in quantity one, but shipping from Mouser or Digikey will always kill you if you only buy one part at a time. Instead, [Ryan] found a supplier for five of these MOSFETs for $6 shipped. This was a good deal and a bad move because those new parts were fakes. Now we have an opportunity to play spot the fake MOSFET and learn that it’s all about the supply chain.

Spot the fake

To be fair to the counterfeit MOSFET [Ryan] acquired, it probably would have worked just fine if he were using his radio for SSB voice. [Ryan] is using this radio for digital, and that means the duty cycle for this MOSFET was 100% for two minutes straight. The fake got hot, and the magic blue smoke was released.

Through an industry contact, [Ryan] got a new, genuine IRF510 direct from Vishay Semiconductors. This is a fantastic opportunity to do a side-by-side comparison of real and counterfeit semiconductors, shown at right. Take a look: the MOSFET on the left has clear lettering, the one on the right has tinned leads and a notched heatsink. [Ryan] posed the question to a few Facebook groups, and there was a clear consensus: out of 37 votes, 21 people chose the MOSFET on the left to be genuine.

The majority of people were wrong. The real chip looked ugly, had tinned leads, and a thinner heatsink. The real chip looked like a poor imitation of the counterfeit chip.

What’s the takeaway here?  Even ‘experts’ — i.e. people who think they know what they’re talking about on the Internet — sometimes don’t have a clue when it comes to counterfeit components. How can you keep yourself from being burned by counterfeit components? Stick to reputable resellers (Mouser, Digikey, etc) and assume that too good to be true is too good to be true.

Filed under: hardware

Improving the Accuracy of Gas Sensors

via hardware – Hackaday

If you need a sensor to detect gasses of some sort, you’ll probably be looking at the MQ series of gas sensors. These small metal cylinders contain a heater and some electrochemical sensor. Wire the heater up to a voltage, and connect one end of the resistor to an ADC, and you have a sensor for alcohol vapors, hydrogen sulfide, carbon monoxide, or ozone, depending on which model of sensor you’ve picked up.

These are simple analog devices, and as you would expect they’re sensitive to both temperature and humidity. [Davide Gironi] wanted a more accurate gas sensor, so he’s diving into a bit of overengineering and correlating the output of these sensors against temperature and humidity.

There’s a difference between accuracy and precision, and if you want to calibrate gas sensors, you’ll need to calibrate them against something. Instead of digging out a gas sensor of known precision, [Davide] took the easy way out: he graphed the curves on the datasheets for these sensors. It’s brilliant in its simplicity.

These numbers were thrown into R, and with a bit of work, [Davide] had a look up table of various concentrations of gasses plotted against certain resistances. In testing these sensors, he found a higher correlation between humidity and temperature and gas concentrations, which one would expect.

The files for these sensors are available on [Davide]’s website, and he included a neat little video showing everyone what went into these calculations. You can check that out below.

Filed under: hardware

Old Part Day: Voltage Controlled Filters

via hardware – Hackaday

For thirty years, the classic synths of the late 70s and early 80s could not be reproduced. Part of the reason for this is market forces — the synth heads of the 80s didn’t want last year’s gear. The other part for the impossibility to build new versions of these synths was the lack of parts. Synths such as the Prophet 5, Fairlight CMI, and Korg Mono/Poly relied on voltage controlled filter ICs — the SSM2044 — that you can’t buy new anymore. If you can source a used one, be prepared to pay $30. New old stock costs about $100.

Now, these chips are being remade. A new hardware revision for this voltage controlled filter has been taped out by the original hardware designer, and these chips are being produced in huge quantities. Instead of $100 for a new old stock chip, this chip will cost about $1.60 in 1000 unit quantities.

The list of synths and music boxes sporting an SSM2044 reads like a Who’s Who of classic electronic music machines. E-Mu Drumulators, Korg polyphonic synths, Crumars, and even a Doepfer module use this chip in the filter section. The new chip — the SSI2144 — supposedly provides the same classic tone but adds a few improvements such as improved pin layouts, an SSOP package, and more consistent operation from device to device.

This news follows the somewhat recent trend of chip fabs digging into classic analog designs of the 70s, realizing the chips are being sold for big bucks on eBay, and releasing it makes sense to spin up a new production line. Last year, the Curtis CEM3340 voltage controlled oscillator was rereleased, giving the Oberheim OB, Roland SH and Jupiter, and the Memory Moog a new lease on life. These chips aren’t only meant to repair broken, vintage equipment; there are a few builders out there who are making new devices with these rereleased classic synths.


Filed under: hardware, musical hacks