David Scholten's pages

Separate from my automatic watering systems, these 10 water circuits
(controlled by switches) do the following: Fill/empty the turtle tank, clean
3 gutters, mist 4 things (2 fences, air-con & people), water the roof and
blast the lawn (fun!).

Using only resistors, diodes and a capacitor to control a relay, this
module delays the pass-through of a USB device by 5 minutes. Some
devices simply REQUIRE that they be plugged in after windows has
booted! I WILL NO LONGER YIELD TO YOU.

Controls, powers & interfaces with various pieces of lab equipment.
Contains onboard processing, OLED, triple power converters, power
protection, buttons, buzzer. I/O is primarily terminal headers and BNC
connectors. The micro is the Teensy 4.0!

This DC/DC converter takes 5V from the Teensy 3.6 USB supply and
converts it to a voltage of up to 24V. The balanced string of eight 50F/3V
capacitors (total: 1800J) allows for bursts of currents of 10A+ and very
simple/slow voltage regulation.

At uni I worked on multiple different ground-based object avoidance
robots for internal competitions. I usually did the electronics in the group.
See:

This self-oscillating class-d audio amplifier was not my design. However,
what was special about it was that it was the first switching power
converter I ever constructed. This made it the defining project that
shaped the direction of my career.

This old thing had an output of +/-30V@3A and an auxiliary output of
+/-12V@1A. It basically powered the majority of my breadboard projects
early on (mostly audio related). It even had a variable speed fan
controlled by the heatsink temperature!

To those projects that failed, frustrated or outright exploded; To the
projects that ended up being redundant duplicates, ultimately teaching
me nothing new... You won't be missed. Seen in picture: The 450 RC heli
that exploded in flight. RIP.

Although there was no auto pilot, this old custom FPV quadcopter had
IMU based stabilisation, stupidly bright LEDs, some basic instrumentation
and a video downlink that made it quite enjoyable to fly around with the
good old "Fatshark" goggles.

This module takes an audio signal, splits it into low, mid & high
frequencies and then pulses 3 different sets of 10-segment bar graphs
(each segment is 8 blue LEDs in series). With the other components
included I had to solder 600+ total pins!

I needed to drop the voltage of various supplies in a simple and fun way.
This device performs a adjustable fixed voltage drop of 0-25V at
ludicrous currents. The massive heat sink and 10W fan allowed for 100W+
of dissipation (it's a hairdryer).

A very old "relaxing" audio amplifier project with an input powered from
+/-12VDC (SLA batteries). The audio signal is sent through an OPA2134
preamp and then to a BD135/BD136 power stage. With zero bias current,
it relies entirely on feedback!

Using Solidworks and a 3D printer I created a "slab" to sit below the
computer that housed: Two PCIe boards, mini-to-PCIe converters/"risers",
a fan/filter, a ventillator port, power entry (fan) & a modified computer
hatch cover. Very tedious...

With a USB/BNC I/O, this box switches the BNC output from 0V to 5V
when the emergency stop button is pressed. Doing so also switches the
LED indicator from red to green. Printed in 4 colours using the Prusa
MK3S MMU2S, it simply looks beautiful!

This PCB is basically a custom wireless phone charger designed to
power/communicate with another module. The micro utilised is the new
Teensy 4.0 and the switching MOSFETs are PN: "RJK0855DPB". 80V,
30A, 11mohms & 10/20Vgs 35nC gate? Yes please!

This PCB turns on a high speed LED as fast as practically possible. Using
a fast MOSFET to charge the inductor current down one path, it can
quickly divert that current through the LED path when needed. LR decay
allows for a peak/cont. current.

This module contains a PCB that interfaces a piece of legacy analogue
hardware with the USB standard. The enclosure features 2 OLED LCDs, 3
LED buttons, a power switch, fuse holder, 3-state LED, 2 fans, 2 I/O row
segments, 3 BNCs & a USB port.

These nodes contain a computer supported by the necessary hardware
to allowed ruggedised, reliable and rapid deployment for node to node
networking with remote operation in mind. 32 system level I/O cables
have been patched to the front panel!

Need rugged I/O accross a network? These boxes will take an input logic
state at any one node and replicate the state at all the other nodes via an
ethernet port. Local signal in > Ethernet > Remote signals out. (Main PCB:
Denkovi DAEnetIP3-ET)

Using Fusion 360 for the two-part 3d-printed enclosure, this (electrically)
simple project contains 8*AA batteries (12V), a DPDT on/off/on switch, a
wireless relay module/remote, a LOUD two-tone piezo buzzer and a
volume control potentiometer.

We developed a unit to test motherboard PCB assemblies semiautomatically
through the use of test pins, relay boards, loads banks,
LabJack DAQs & programmable power supplies. A PC running LabVIEW
was used for interfacing & control.

We developed two units to test the functionality of complete product
assemblies. The tester checks wiring logic, device output voltages and
harness impedances. All processes are controlled and logged via a
μcontroller & PC terminal.

We developed a unit to test 5x5 arrays of panelised PCB assemblies.
This tester contains test pins, relays, light sensors and light piping - All of
which is duplicated 25 times and addressed via a μcontroller through
demultiplexers.

Given existing test hardware and a complete assembly, I was tasked with
creating a μcontroller control module for automation.
Features/interactions include an RS-485 MODBUS line, a USB keyboard,
an LCD screen and an SD card reader.

A copper disc with three closely positioned 3-phase solenoids that
induce a rotational torque in much the same way as the modern
induction machine does. It is driven by a 12V, 3-phase inverter made of
spare parts:

A weapon-less pusher type, this 150g 3D printed robot is defined by its
interchangeable armour, absurdly fast/powerful 15W motors, wide tyres
and gyro stabilisation. A demo of the robot (gyro ON) can be seen at:

Using 45 Watts of PV power (~18V MPP), two 30W Peltiers (0-9V), an
MPPT buck converter (IV-matching) and a temperature switch (anti-frost),
water is slowly collected at the cold-side heat sink where it falls through
a funnel and into a bottle.

A very old project. By using a single VU meter IC (LM3915?) and a
another IC that sequentially connects the columns of LEDs to ground (i.e.
the time scale), the VU meter effectively "sweeps" across the waveform in
a quick succession.

To control the discharge of my 50V/0.3F capacitor bank in a modular
fashion I took an 800A peak thyristor, a piezo buzzer, a 9V battery and a
momentary switch and then stuffed them all into an off the shelf project
box with power I/O terminals.

A 60W 12V plug pack power supply is boosted to 24V, which is then fed
to a 50W class-D amplifier with bluetooth audio receiving capability. The
output is then split at 3.8kHz with a 2nd order high & low pass filter for
the 8Ω tweeter & woofer.

Two cascade Peltier units (top: adjusted to ~36W, bottom: ~72W) This
draws about 9-10 amps total at 12V. Heat pump transfer is 15W optimally
and the minimum cold side temp reaches -30°C. See:

32V & 4A input, 600kHz switching frequency and a soft start relay. These
amplifiers are very hard to design but are very rewarding when they are
done right. I would highly recommend them for anyone that wants to
learn about power electronics.

Contains 6 servos, a text-to-speech unit, glowing eyes, audio reactive
LEDs throughout, a spinning gun, power supply, audio amplifier, music,
transformer, a brain and manual controls! See it here:
www.youtube.com/watch?v=E8185o7we04

A 1-30V, 6A linear power supply housing a TO-3 regulator, circuit and a
serious heat sink. Features include: A soft start relay, a temperature-based
two speed fan, under/over voltage alarms and disconnects,
various displays & indicators + more!

I thought it would be a fun idea to visualise some math functions as 3D
prints. The MATLAB script that I created took an equation, converted it to
a surface plot, added a solid base underneath and generated an STL file
for 3D printing.

I put together 4 control boards and 4 H-Bridge power stages to make a
decentralised multilevel cascaded grid-tied inverter. The input is DC
power which is converted and sent back to the grid. Effectively, this
system educates and heats the room.

Now you think I would have realised that a serious H-bridge should be
operable from 3.3V. Well I stuffed that up and as a result I needed a way
to allow my 3.3V microcontrollers (Arduino Due) to interact with my 5V Hbridges
and their sensors.

The final version of the H-bridge for the cascaded inverter of my PhD.
This final version was much more robust, had a LOT of protection and
other features that made controlling it so much simpler. To date, non of
these boards have failed in use.

During the earlier stages of my PhD I realised I would need H-bridges for
my cascaded inverter at a later point. I went about designing and
constructing a very early version of the H-bridge to test. This was the first
time I had used Altium.

The Align Trex 550 is a 1400W model helicopter with a body length of 1
metre and a battery life of 10 minutes. Assembling this allowed for a deep
understanding of the mechanics of helicopter flight and maintenance.
Very educational!

My first "serious" amplifier project! A dual 15W class AB amplifier with a
bias current of about 1A per channel (that's a total standing heat
dissipation heat of near 60W)! Summary: Dual Transformer-->Rectifiers --
>Caps-->+/-15V-->Amp ALSO FAN!

A 200W remote control car with video/audio transmission. Features
include a front/rear camera (with pan/tilt), front(10W)/rear(1W) headlights,
rear microphone, 900MHz video with OSD, 2.4GHz control, and a fluffy
doll for attracting children.

Using a micro-controller and the insides of a remote from a network of
wireless mains relays, I automated the devices in my room. There is a
motion sensor, a wireless "bedtime" switch and a set of pre-programmed
configurations.

A 50V capacitor bank made up of 10mF caps (31 of them). The total
maximum energy is 387.5 joules. There is a controllable bleed resistor
and voltage/current multimeters powered by a single 9V battery. The
ultimate DC-link capacitor!