Stripboards

Most of the DIY I do, I do on stripboards. These are fairly cheap, and I don’t need to deal with chemicals for etching PCBs. The stripboard is easy to use, but when the circuit is very complex or when many digital ICs are used, the stripboard layout tend to be messy, complicated, and big. I prefer to use the stripboard that has copper tracks running along the entire length of the stripboard.

First I draw the layout, usually by hand on a checkered paper. These draft layouts are ugly, but they do the work. But sometimes I use a illustration software to make a more easy to read layout… Normally, I see the copper tracks as going horizontally when making the layouts. I always draw all connections, even marking the copper tracks between components (when drawing by hand), that makes it more easy to see all connections and discover errors. Then I mark all cuts/breaks in the copper tracks with an “X”. I usually try to remember to add component values to the layout, as this will make the soldering process much faster. It is also good to remember to double check pins on ICs and size of trimpots and capacitors (etc) to make sure that the layout actually matches the components.

Stripboard layout

Stripboard layout

A more easily read layout...

A more easily read layout…

When cutting the stripboard to the correct size, I use a small hacksaw to cut the board to the right size. I use a small grinding file to trim the edges to remove any leftovers from the sawing that might create shorts between copper tracks.

Cutting and fixing the edges of the stripboard

Cutting and fixing the edges of the stripboard

Then I usually use a pen to make some markups on the board. This will help me when placing the components. A tip is to count the holes (the number of holes in between components) several times (!) before making a mark, to avoid mistakes.

Making marks on the stripboard helps when placing components

Making marks on the stripboard helps when placing components

When some components are soldered in place, I use a 3mm (or something about that size) drill to break/interrupt the copper tracks on the stripboard. I do this by spinning the drill between my fingers, and then I use a sharp knife to cut off any burring. A good idea could be to mark all cuts with a red pen on your layout, then count them on the paper, and when all cuts have been made, count them again to make sure that you’ve made all interrupts.

Cutting the copper tracks under the stripboard

Cutting the copper tracks under the stripboard, use a drill and a sharp knife

Use a magnifying glass to check all interruptions, and while at it check the soldering as well! If you’re careful, you can build any module you want with stripboards. I’ve built anything from VCAs to LFOs, via VCFs and clock pulse dividers.

Diffusing LEDs

Today it’s very cheap to buy LEDs, and one can easily find them in many different colors, from single color LEDs (orange, red, white, blue, green, yellow, violet, and so on) to two or three colored LEDs. However, at least at the component vendor I usually buy from, most of the cheap LEDs are clear and not diffuse that I want. For example you can buy a bag with 25 LEDs for about €2 (or $2.30). That’s perfect for your DIY sequencer! However, most often these cheap LEDs are clear… But, it’s actually easy to make a clear LED into a diffuse LED.

By using a very fine, like P180 or P220, sandpaper/abrasive paper you can easily rough up the surface of the glass on the LED. Make sure to make this fully around the LED, and try to make the grinding smoothly without any deeper parts or leaving any clear parts out. I usually do this by having the sandpaper on the sharp edge of a table, and holding the LED in my fingers moving it back and forth while slowly turning it. Now you have a nice diffuse LED.

Two clear LEDs. The right one has been diffused using a fine sandpaper.

Two clear LEDs. The right one has been diffused using a fine sandpaper.

If the sandpaper is too rough, the somewhat larger sand particles might create a less smooth surface of the LED. There will most probably be deeper strokes in the glass surface of the LED. This in turn will affect how the light emits from the LED. These deep crevices might be clear on the inside and therefore they will affect the direction of the light. But, wait! This might be a cool effect! LEDs with crystal patterns! Maybe, since the LEDs are so cheap, you could try to use a small and sharp grinding file, to create cool light patterns in your modular!

Pseudo-random LFO

Sometimes there’s a need to get random voltages, you can do that with a S&H and a noise source (see this previous post), or you could do it with a pseudo-random voltage source. This is a pseudo-random control voltage source that uses four square wave generators, of one with controllable frequency, and mixes these four signals to form one moderately random pulse wave at the output. This illustration shows the mix of four square waves with different frequency.

Summing square waves. From Digital Generation of LFO’s for Modulating Effects. Copyright 2000 R.G. Keen

My design of a pseudo-random LFO is inspired by the design by R.G. Keen as well as a of Ken Stone’s design, and there are probably many other similar designs out there. It has four controls (Coarse rate and fine rate, Range of the pseudo-random CV (1-10V), and Slew (stepped CV or smooth CV), it also has two outputs (pseudo-random CV out and pseudo-random clock out (positive going clock pulses at +5V)).

pseudo-random-lfo

Pseudo-random LFO

The module uses +5V, +12V, GND, -12V, and needs a +5V option installed in the modular system, or have a +5V voltage regulator (e.g. 7805…). It would also be possible to use a HEF40106B Hex inverting Schmitt trigger instead of a 74HC14, and this would remove the need of +5V.

4-channel mixer and multiple

When mounting different modules in one of my cabinets I ended up with a small empty space, 3HP. The reason for this is that I mixed “standard” 8HP modules (DIY and Doepfer) with 5HP and 10HP modules (Eowave). Since the space is too small to add much controls on a front panel, I thought about adding a small blank panel covering the empty space. But, on the other hand, you’ll always need to be able to split and sum signals, why I built a small 4-channel mixer and multiple. The module mixes up to 4 signals without any level controls, and distributes the mix to 4 independent buffered outputs.

mixmulti_schema

4-channel mixer and multiple

The module works fine for both audio and CV signals, and can easily be soldered on stripboard.

4-channel mixer and multiple

4-channel mixer and multiple soldered on two small stripboards

 

Mod wheels

I had two mod wheel from an old MIDI keyboard laying around, and thought it would be nice to have another control source in the modular, something that’s not that small that Eurorack tends to be… However, a mod wheel with only a volume control felt a bit boring, so I decided to add something else. One of the mod wheels had a spring making it return to the middle position and made it into Pitch bend wheel, with controls for the pitch bend range. I added three trim pots to adjust DC offset as well as range, it’s certainly not perfect but works good enough.

cv-wheel_schematic

Pitch bend wheel

It turned out a rather nice module, not very sexy or exciting, but useful. The second mod wheel did not have a spring, but stayed at the set level.  To make it into something more exciting I added an internal clock source. There’s also an input for an external clock source for syncing the module with other modules. The clock signal in turn, controls a stepped triangle or ramp wave which is sent via the input to the wheel and then (buffered) to the output. If any signal is connected to the input, this will override the internal stepped wave, and then the module might be used as an buffered level control.The stepped output might be used as an arpeggiator where the mod wheel sets the range of the arpeggio. An external CV quantizer i highly recommended to get correct tones…

cv-wheel2

CV wheel with built in stepped LFO

Both these modules turned out nicely. They are useful, and fairly easy builds, in the way I enjoy to make music with my modular setup.