Category: Electronics

ESP32 WROOM32 – A possible fix for failure of auto-program facility

Espressif’s esptool has a facility to automatically put the ESP32 into bootloader mode using the DTR and RTS signals of the serial interface.

For whatever reason, it is very unreliable. There are many schematics of knockoffs of Espressif’s original DevKits.

Above is the schematic of one of the larger makers of ESP32 modules, AI-Thinker. The auto-program facility is implemented in the logic gate arrangement at right top of the left top block. Continue reading ESP32 WROOM32 – A possible fix for failure of auto-program facility

Last update: 17th November, 2020, 2:10 PM

Battery contact corrosion on digital calipers

Corrosion of battery contacts in all manner of things due to leakage from the batteries is a growing problem as we seem to accumulate more and more devices that contain batteries and it becomes a chore to replace batteries by their expiry date.

Replacing batteries by their expiry date does not guarantee freedom from leakage related corrosion. The battery market is flooded with counterfeit product and it is hard to know what is genuine, even from apparently reputable suppliers.

Above is a cheap Chinese digital caliper that was damaged by leakage from a brand name (Duracell) SR44 cell. The characteristic green residue has been cleaned from the positive contact with an alcohol soaked cotton bud, and then the contact scratched with a Burgeon 2834C fibre glass scratch brush (below) to remove remaining corrosion products whilst vacuuming to extract as much of the residue as possible. Again, a wipe with a clean alcohol soaked cotton but leaves the contact as clean as practicable. These scratch brushes are extremely effective, one needs to avoid over use which removes more plating than desirable. Continue reading Battery contact corrosion on digital calipers

Last update: 27th October, 2020, 10:05 AM

Photo Voltaic Array – unbelievable efficiency from Chinese sellers

A friend recently purchased one of the many PV arrays advertised on eBay only to be disappointed.

A common metric used to evaluate cell technologies is conversion efficiency with 1000W/m^2 insolation. Most popular products are monocrystalline silicon technology which achieves 18-25% efficiency on an assumed 1000W/m^2 insolation.

If we look carefully at the above panel advertised as 200W, the active PV area is less than the frame size, probably \(A=0.93 \cdot 0.63=0.59 m^2\). We can calculate efficiency \(\eta=\frac{p_{out}}{1000 A}=\frac{200}{1000 \cdot 0.59}=34\%\), nearly double expected efficiency for monocrystalline cells. Continue reading Photo Voltaic Array – unbelievable efficiency from Chinese sellers

Last update: 14th October, 2020, 2:53 PM

Review of iFIX RT300M v2 LED tester

In other posts on LED luminaires, I identified the need for a test device for LED strings of up to 200+V at currents up to 280mA.

There are quite a number of competitive devices in the market, the article is a review of the iFIX RT300M v2 (which is also sold under other brand names, they may or may not be sourced from the same factory… the Chinese are copyists).

 

I purchased one of these devices, and it was faulty on delivery. The output voltage never rises above 0.3V, determined to be a hardware fault. With eBay’s intervention, a full refund was obtained without returning the faulty unit which turned out to be a small blessing later.

The v2 RT300M has a button on the top edge of the device. Continue reading Review of iFIX RT300M v2 LED tester

Last update: 10th August, 2022, 7:48 AM

Calculation of impedance of a ferrite toroidal inductor – from first principles

A toroidal inductor is a resonator, though it can be approximated as a simple inductor at frequencies well below its self resonant frequency (SRF). Lets take a simple example, a ferrite toroid of rectangular cross section.

From the basic definition \(\mu=B/H\) we can derive the relationship that the flux density in the core with current I flowing through N turns is given by \(B=\frac{\mu_0 \mu_r N I}{2 \pi r}\). Continue reading Calculation of impedance of a ferrite toroidal inductor – from first principles

Last update: 19th January, 2021, 10:38 AM

Arduino Nano – FT232RL test pin floats

The Arduino Nano leaves the FT232RL TEST pin floating which may give rise to initialisation and communications problems.Grounding the test pin by bridging pins 25 and 26 with a small solder bridge seems to overcome the problem.

 

NanoMod

Above, a fixed chip.

Last update: 17th July, 2020, 9:59 PM

Oyster conversion – #2 – 24W

Conversion of oyster luminaire to LED discussed a first conversion effort. This article describes a conversion of a oyster that used a T8 32W flourescent tube.

First step was to strip the magnetic ballast, power factor correction capacitor (if fitted), clips for the tube, labels that are misleading, and to check / provide the needed protective earth connection.

The LED plate used is that reviewed at LED plate analysis – 24W round plate with driver but with a new driver that delivers 260mA (though rated at 300mA).

Above is the 24W LED plate. The plate has 48 0.5W 5730 LEDs in a 24×2 configuration. If we allow that the 24W rating is total input power, driver loss is typically around 2W so the LEDs themselves will draw 22W. We expect that the voltage at 22W will be around 80-85V, and will require ~275mA current. The original LED driver supplied (180mA) is not capable of that current and was discarded. A nominally 300mA LED driver was procured for about $10 for five, and they fall short, delivering 260mA but that is good enough for this implementation. Continue reading Oyster conversion – #2 – 24W

Last update: 4th July, 2020, 12:08 PM

LED plate analysis – 24W round plate with driver

This article reviews a 24W LED plate and driver commonly sold on eBay and Aliexpress for around $12.

Above is the 24W LED plate from the sellers pics. The plate has 48 0.5W 5730 LEDs in a 24×2 configuration. If we allow that the 24W rating is total input power, driver loss is typically around 2W so the LEDs themselves will draw 22W. We expect that the voltage at 22W will be around 80-85V, and will require ~275mA current. It is shown here with a 220mA LED driver or 80% of what is required for 22W. Continue reading LED plate analysis – 24W round plate with driver

Last update: 3rd July, 2020, 11:16 AM

AD9833 / PllLdr checkout

PllLdr is a generic microcontroller to load a PLL chip’s configuration registers using SPI. SPI is used by many PLL and DDS chips, data format and content varies from chip to chip.

This article documents checkout on an ADF9833 DDS chip.

The test was made on an inexpensive module purchased on eBay for about A$3 posted. This board has a 25MHz clock oscillator, but be aware they are sold with other frequencies as well, and is usable to about 40% of the clock frequency.

Above is the test board. It does not contain any form of output filtering, it really is bare bones. Continue reading AD9833 / PllLdr checkout

Last update: 25th July, 2020, 5:48 PM