This article documents design of a capacitive transformerless power supply for operating low voltage, low power logic from power mains. The intended application is PAROT (Duffy 2013), though it has potentially wider application.
(Microchip 2004) gives a method for design of a capacitive transformerless power supply for operating low voltage, low power logic from power mains. The equations seem simplistic for a circuit whose apparent simplicity belies the complexity of an optimal design that properly tolerates supply voltage and load variations. For that reason, a SPICE simulation was used to refine a design.
The immediate application is for the PAROT chip driving a 40A SSR.
Above is measured characteristic of a Fotek 40A SSR, it seems typical of several similar types on hand. It appears that much smaller SSRs in the 2A range require fairly similar current. Continue reading Transformerless power supply for PAROT
Fox flasher MkII – owenduffy.net described an animal deterrent based on an STC 8051 microcontroller and running from a single LiPo cell.
This article describes a further development using a solar cell, shunt regulator, 1S LiPo cell with protection board, and two high power red LEDs.
Above, the unit constructed in a medium size Jiffy box, and a 6V 0.6W PV panel fixed to the top with silicone adhesive. The LDR is fixed to one end with silicone adhesive.
Two SM 1W red LEDs are fitted to opposite sides. They are 120° LEDs, the holes are countersunk to provide for light dispersion and the LEDs clamped to the inside with small brass brackets and heat sink rubber, a little silicone adhesive seals the holes. Continue reading Fox flasher MkII – high power 2 LED solar powered beacon
This article documents a field strength survey of an M40-1 short helical vertical on 40m.
This test is more a feasibility study of the experimental method and apparatus than an absolute measure of the antenna.
The antenna under test is described at AUT – MobileOne M40-1 40m helical.
Field strength was measured using a small square untuned loop and VK3AQZ RF power meter (RFPM1), and data was captured using A prototype data logger for RFPM1.
VK3AQZ RF power meter (RFPM1) described my build and calibration of the RFPM1.
Above is the RFPM1, shown with two probes, but only one probe is required for this procedure, the other is disconnected. The RFPM1 directly reads input power in dBm.
The loop antenna used was described at (Duffy 2007). It is a small square loop (600mm sides) fed in one corner with a 1:1 voltage balun. Continue reading Field strength survey of an M40-1 short helical vertical on 40m
The growing popularity of 5V plug packs and Li-ion power banks with USB A connectors provides a convenient source of power for some projects, and a USB-A to 5.5/2.1mm DC cable is a possible connection option.
Scouring eBay turned up some sources, but one can never assess the quality of the things because usually there are no meaningful specification offered, and lets face it, they are Chinese.
Above are two sample 1m cables that I purchased, the left one for about A$1, and the right for about A$3.50 (posted).
Loop resistance of the cables was measured with Kelvin probes to assess their current carrying capacity from a voltage drop perspective.
DC loop resistance of the one on the right was 0.16Ω, so the maximum current for a 5% voltage drop is 5*0.05/0.16=1.6A… not quite a 2A rating.
DC loop resistance of the one on the left was 3.3Ω, so the maximum current for a 5% voltage drop is 5*0.05/3.3=0.075A… not even a 100mA rating.
This is not surprising, experience with USB-A to USB-micro cables has revealed similar variation, and an explanation why so many of these cables are hopeless in battery charging applications.
Browsing eBay for some high power LEDs for a current project created frustration in trying to wade through the stated performance figures (to they extent that they can be relied upon).
LEDs are often headlined as having some luminous intensity in candelas, but while that might seem to be a good measure of the ‘brightness’ of the LED viewed on-axis, it gives no information about the spatial distribution off-axis and the total luminous flux output or flux density.
I wrote a little online calculator that can be of assistance in finding the total luminous flux and flux density give luminous intensity and apex angle, Calculate luminous flux (lm) from luminous intensity (cd) and apex angle (°). (Note that specified luminous intensity is usually on axis and should be discounted by perhaps 20% to provide an average luminous intensity over the cone angle.)
An example, an eBay seller advertises:
Source Material: InGaN !
Emitting Colour: 0.5W 10MM HI POWER White 0.5W LED
LENS Type: Water clear
Luminous Intensity-MCD: Typ: 290,000 mcd
Reverse Voltage: 5.0 V
DC Forward Voltage: 3.2 ~ 3.4V
DC Forward Current: 100mA
Viewing Angle: 40 degree
Lead Soldering Temp: 260¡ãC for 5 seconds
Power Dissipation: 500mW
Does it appear rational? Lets calculate average luminous intensity at 80% of 290cd, 232cd. Lets assume the viewing angle is the half power beamwidth.
Above is a calculation from the specifications. Of concern is the calculated luminous efficiency of 266lm/W, it is perhaps three times or more the expected value, so it questions the accuracy of the claims. Even at 0.5W input, the luminous efficiency is unrealistically high. Continue reading Making sense of LED output figures
This article reports an experiment to evaluate the usefulness of precision GPS for the purpose of location data for automated antenna field strength surveys.
The experiment was conducted with the rover located in a fixed location 13km North of the reference station at Symonston and with very wide view of the sky, about 7:00 am 07/04/2016.
Only GPS satellites were used for the rover.
The software was RTKLIB v2.4.3b8.
The GPS was a UBLOX LEA-6T with a small patch antenna (as sold for small UAVs). The LEA-6T provides binary data as used by RTK for carrier phase measurements. Above is the GPS and a USB-RS232 adapter. Continue reading Precision GPS experiment #1
On review of the Ultrafire XML-T6 torch, I found the mode switching / mode memory so dysfunctional that it rendered the torch useless in my evaluation.
This article describes a work around that makes the thing usable (IMHO). Continue reading Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’
Claims of performance of LED torches become more extravagant by the month it seems.
Above is an Ultrafire XML-T6 LED torch purchased on eBay for about A$25 posted. The seller claims “CREE T6 2000lm LED Zoomable Torch Flashlight 2 x 18650 4200mah AAA Batteries”. Continue reading Ultrafire XML-T6 torch review
I purchased a torch (flashlight) on eBay recently. It was described as using CREE T6 LED array, and supplied with two 4200mAh 18650 Li-ion rechargeable batteries with charger for A$25 inc post.
Above, the cells are clearly marked 3000mAh, way short of the advertised 4200mAh… but what is their actual capacity.
Above are the results of discharge tests, the first digit is the cell number and the second is the test. The first test is charged with the supplied charger, the second test is with my charger. Continue reading Chinese 18650 Li-ion cells – Ultrafire capacity test
Readers may have seen the Elitech RC-4 logging thermometer in some of my articles, and data for many articles was collected using it.
It came also which an external sensor which has been very useful in many of my experiments. Continue reading Elitech RC-4 logging thermometer