BLHeli 14.8 damped light and active freewheeling

Aficionados of BLHeli call out the benefits of “damped light” and “active freewheeling”, terms coined by BLHeli’s author.

Since these are terms invented by BLHeli, so you might wonder whether they are truly innovative or just marketing hype for existing techniques.

Lets go to the BLHeli manual for an explanation.

Pwm damped light mode adds loss to the motor for faster retardation. Damped light mode always uses high pwm frequency. In damped light mode, two motor terminals are shorted when pwm is off

Taking the last statement first, in fact, what happens that as that during the OFF phase of the PWM drive, the high side FETs at both ends of the winding are turned ON. One FET is on for the whole phase, and the other one switches on a short time after its corresponding low side FET turns off. The short time is to allow the low side FET to cease conducting, otherwise both high and low side FETs would conduct at the same time, a current from battery +ve to -ve via the two FETs. There is a corresponding pause at the end of the PWM phase. The time delays allowed depend on the driver circuitry and FET performance, they are specified in the firmware  for a specific and don’t necessarily apply to a pin compatible ESC.

This technique is known in the wider community as COMPLEMENTARY PWM, a very standard technique. Continue reading BLHeli 14.8 damped light and active freewheeling

LED lighting woes

Pressed to replace working lighting with so-called ‘energy efficient’ lighting by well-meaning but narrow sighted conservationists, I recently replace about 25 CFL lamps with 12 LED MR16 lamps.

They have started failing now after a couple of years of service, perhaps 4,000 hours of service. So much for the claims of 100,000 hours… clearly preposterous.

In an effort to identify which of the switched mode power supply or LED assembly was the problem, I tried to substitute LEDs to different power supplied.

That was not a good idea, lets look at the anatomy of your typical Chinese junk MR16 LED.

Above is the complete 12W MR16 lamp with GU5.3 bipin connector on the back. Continue reading LED lighting woes

TV upgrade – MER optimisation

At TV upgrade I reported a change in TV antenna pointing to a different and distant transmitter, and gave a Spectrum Analyser plot at the main TV receiver.

At that time, I adjusted the antenna accurately (within 1°) based on compass heading, but antennas are not perfect and two significant path obstructions may have bearing on best signal.

I could have run up and down the ladder making small adjustments and observing amplitude or better, RF S/N on the Spectrum Analyser but that is tedious and suboptimal so I purchased a DVB signal analyser.

Importantly, a good DVB analyser gives measurement of not just signal strength, but carrier to noise (C/N) ratio (which is actually RF S/N), Bit Error Rate (BER) and Modulation Error Ratio (MER), the last two very important statistics in optimisation and validation and not available on an ordinary Spectrum Analyser.

MER is calculated as the sum of the squares of the magnitudes of the ideal symbol vectors is divided by the sum of the squares of the magnitudes of the symbol error vectors. The result, expressed as a power ratio in dB, is defined as the Modulation Error Ratio (MER).

MER is a good overall single statistic for quality, but BER is more sensitive to occasional errors, so they are both important.


Above, the DVB analyser (the red device) enables a view of measurements whilst adjusting the antenna. The analyser here is connected to the masthead amp output and of course powers the masthead amp. Continue reading TV upgrade – MER optimisation

Coil32 inductance calculator

A recent online posting gave unequivocal recommendation for the Coil32 Inductance Calculator for application to a ferrite toroidal HF current balun.

Always interested in these things, I tried to download it to evaluate it but there was rigmorol to create an account and aware that I have never downloaded a calculator that handled that specific problem at all well, I was reluctant.

They do however have some online calculators that are supposed to use the same algorithms and methods as the downloadable software, so lets review the one for a toroidal ferrite inductor.


Above is the data entry form, and warning bells sound. The “releative magnetic permeability” field is a simple scalar quantity, but the permeability of most ferrites at HF needs to be considered as a complex value (ie having real and imaginary components). Continue reading Coil32 inductance calculator

TV upgrade

The restack of TV channels, and then the allocation of spectrum immediately adjacent to a 4G mobile site that is 1km away and directly in line with Knights Hill (30km) caused me to rethink our TV source and switched to Mt Gibraltar (5km) to escape the 4G interference.

For whatever reason, the signal from Mt Gibraltar has dropped in level and is intermittently very inconsistent.

So, it is back to Knight’s Hill with a LTE filter to try to alleviate the interference from the in-line 4G site.


Above is the received channels at the TV set with a 6dB 75/50 pad inline. After the last restack, the five desired are now at least 90MHz lower than the edge of the 700MHz LTE (4G) allocation, and with an LTE filter in the masthead amplifier, it seems interference is not noticeable. Signal quality reported by the TVs is consistently 100%.

The spectrum analyser plot underestimates RF S/N due to the system noise floor.

The channels used are 35 (ABC),36 (WIN),37 (CTC),38 (CBN),39 (SBS), all 250kW. Ch 35 and 39 are on the BA tower, the others on the WIN tower.

If only there was something worth watching!

Small signal diode characteristics

We often use diode detectors at microamp currents, and the question arises as to the type of diode best suited to sensitive detectors.

Setting aside zero bias Schottky diodes which are a topic in themselves, the choice is typically between commonly available germanium, silicon and Schottky signal diodes.


Above is a plot of the I,V characteristic of four common signal diodes at currents up to 1mA. It can be seen that at currents below 600µA, the forward voltage drop of the humble 1N34A germanium diode is lower than the others. The 1N270 is an alternative if you really need its higher breakdown voltage. Both of these diodes are reasonably easy to obtain, and cheap at that.



AD9850 / AD9851 initialisation using PllLdr

A note on using PllLdr with AD9850/51 DDS chips.

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.


The AD9850 powers up in parallel load mode, and AD gives advice on how to get it into serial load mode (as you would use with PllLdr). A slightly briefer method seems to work reliably and is described here. Continue reading AD9850 / AD9851 initialisation using PllLdr

ADF4351 / 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 ADF4351 PLL chip. The ADF4351 is a wideband INT-N / FRAC-N synthesiser with integrated VCO, output covers 36-4400MHz (continuous).

The test was made on an inexpensive module purchased on eBay for about A$33 posted.


Above is the test frame. At the left is a PllLdr prototype running on 5V, then a 4 channel 5V/3.3V  level converter, the ADF4351 module and at the right a power supply board. The level converter is not needed if the PllLdr chip was run on 3.3V, it was used to test a ‘worst case’ scenario.


Above, a close up of the board.


As can be seen, the connectors are not designed for the 0.8mm PCB used, and the right hand connector has not been connected to the track. Chinese ‘quality’.

The onboard 25MHz crystal oscillator was used as the reference, but a 10MHz reference from a GPSDO could be used for high accuracy. Continue reading ADF4351 / PllLdr checkout

Toshiba alkaline AA leakage problems

I have used Toshiba alkaline cells in several sizes for many years (decades) and had not encountered one leaked cell… however in the last few months I have found 8 AA cells that have leaked in different devices.

The leakage has always had the same failure.

toshibaaa03Above is a view of the -ve end of the battery, ground through to expose the inner structure.

The failed batteries have leaked corrosive electrolyte, and they have all split around the circumference of the battery in the region indicated by the red arrow above. The split is common half way or more around the cell, the green seal and remnant of the rolled over case is  there, split away from the main case and covered in corrosive electrolyte residual.

This is not a failure of the green seal material, but rather the case fails.

It fails either due to internal corrosion, os weakness of the forming process. It is not clear that this area should be exposed to electrolyte anyway, so the corrosion might result from some other internal failure that releases electrolyte.

Enough reason to remove them from all devices and NEVER use these cells again.

Fan controlled by humidity sensor – pre implementation data gathering

This article documents measurements of temperature and relative humidity (RH) over 10 days prior to implementing the fan solution to provide a baseline for designing the Fan controlled by humidity sensor.

A RC-4HC datalogger was used to collect temperature and RH measurements over 10 days which included a range of late winter weather, some rain, some fine clear days. The logger was located at 1.5m above floor level in the shed in a relatively clear spot in the middle of the area..

Screenshot - 22_08_16 , 15_53_17

Above is a chart of temperature and RH. The daily RH peaks are typically between 08:00 and 09:30, and pretty much coincide with the minimum observed temperature. There is clearly a lag from outside temperature which would tend to be minimum a few hours earlier, and a lower minimum (there were plenty of frosty days in the sample set). Continue reading Fan controlled by humidity sensor – pre implementation data gathering