I made a couple of picnic tables about 35 years ago. The design was broadly inspired by picnic tables deployed by the ACT administration at the time (local government), it used a galvanised water pipe frame for table and integral seats and hardwood tops.
I kept one of these tables, and the hardwood eventually degraded sufficiently to warrant replacement.
Durable timber has become very expensive, and the choice limited. Red Ironbark (a eucalypt endemic to the forests south east of here), GOS (green off saw) and DAR (dressed all round) was chosen, and stacked in the shed for a couple of years to dry down to 10% moisture content.
The timber was washed down, trimmed and edged, drilled and oiled (Organoil, a naturally drying oil mix), and fixed to the table with 304 stainless countersunk socket head M8 screws and nyloc nuts.
Above, the refurbished table. Total mass is 125kg, about half of that is in the hardwood and the rest in the steel frame.
The table will required replenishment of the oil finish every year, but should be a durable non-toxic lasting finish with that maintenance.
Some of my projects use a single Lithium cell for power, and the ready availability of low-cost battery protection boards offers opportunity for better projects.
Above, a 1S board rated at 4A and which sells for about A$1 posted in lots of 5.
New and good quality
Use BM112 protection chip + AO8810 MOS tube
The protection board is used to protect the battery overcharge, over discharge, so can’t use as a charger,when you want to charge the battery you need to use the dedicated charger,because the protective board has a time to response to the short circuit, can’t to connect too large instant impact current, such as drills and so on
The main performance parameters:
1. PCB Size: 39 * 4 * 2mm
2. Overcharge protection voltage: 4.2750 ± 25MV
3. Over-discharge protection voltage: 2.88 ± 75MV
4. The overcurrent protection: 4-8A
5. Continue working current: > 4A
Note: Only for the equipment which instant start-up current less than 4A,those starting current instant is great, such as high-current motors, drills, etc., are not suitable for use.
Above are protected battery assemblies based on the board and a 1200mAh LiPo (sells for about A$4) and Panasonic 18650 Li-ion 3400mAh (sells for about A$12). The connectors used are 3A rated JST RCY connectors as used in RC battery applications and readily available with tails for way less than A$1 each set.
The 18650 cell has tags spot welded to the battery contact points, the LiPo has contact tags as supplied.
To use these, the power source needs to supply about 4.5V so as to ensure charging when necessary. The power source needs to be current limited unless you choose to depend on the protection boar’s limit.
Further to 18650 Lithium Ion cells on eBay I purchased a pair of Panasonic NCR18650B cells, nominal 3400mAh, from an Australian supplier for about A$22 posted.
Above is a pic of a cell.
Above is a zoomed in view of the same pic with increased contrast. The feint quality control code printed on the underlying steel container is visible. It is usually visible through the jacket on genuine Panasonic cells.
It is always hard to know whether the product is genuine, the Chinese are better at copying the looks than the internals.
The cell was charged, then discharged at 1C on a battery analyser.
Above is the first three discharge cycles, the cell achieved just under 3000mAh to 2.8V, about 93% of datasheet rated capacity of 3200mAH, 85% of the advertised nominal 3400mAh capacity.
The actual discharge curve is fairly similar to the 1C curve from the datasheet.
These cells look more promising than the GTL red 5300mAh cells previously evaluated.
I have been intrigued by the huge number of sellers of very low cost 18650 Li-ion cells on eBay.
Could they be any good?
As a reality check, Panasonic cells around 3000mAh sell through traditional channels here in Australia for around A$20 per cell, there are Australian eBay sellers selling cells advertised as Panasonic for around A$22 per pair posted.
Above, the GTL red LS18650 5300mAh Li-ion cell purchased in a lot of five for $1.30 each (inc post from China). The rated capacity is more than 50% higher than the maximum from brand name products. Continue reading 18650 Lithium Ion cells on eBay
I have successfully implemented a few projects on the STC 15F104E, a Chinese 8051 architecture MCU.
The chip includes EEPROM, and some flexible extensions to the timers which potentially make it more useful than a standard 8051.
I have previously observed that the documentation is poor, and the programming tool is poor.
The project that led to the latest observations was an attempt to implement RC PWM – ON/OFF switch originally on one of these chips as it contained sufficient resources to suit the application. One of those resources was an +/- edge triggered INT0.
The code worked fine, but for only a short and variable period. Essentially, the the main loop was executing fine, the chip stopped triggering the interrupt service routing for INT0 after a variable time from 10s to 1000s… but it ALWAYS stopped working. Cycle the power and the same thing is observed. Continue reading Revised thinking on STC chips
This article describes a remote ON/OFF switch which uses an RC receiver and adapter chip to convert the RC PWM signal into an ON/OFF output. (Suitable RC transmitters are on hand.)
The immediate application is for remote ON/OFF PTT or KEY of a transmitter for field strength testing at various locations.
Remote control hobbies have long used a multi channel digital proportional protocol for control of planes etc. The simplest multi channel receiver has an independent PWM output for each servo.
The PWM signal is a 1000-2000µs pulse with a repetition rate from about 50Hz up to 500Hz or so, the duration of the pulse conveys the information.
The converter chip is a ATTiny25 MCU with firmware that monitors the PWM stream and provides ON/OFF and OFF/ON output pins. For the immediate application, the ON/OFF (or non inverted) output drives a 2N7000 FET with ‘open collector’ output suited to the PTT and KEY lines of most modern transceivers.
The firmware ignores PWM signals with duration outside the range 900µs to 2100µs, and switches ON at 1600µs, and OFF at 1400µs to provide some hysteresis. If PWM input is lost for 125ms, the output will fail safe OFF.
Above is the schematic. The 2N7000 is good for 60V, can handle up to 100mA without a heat sink, and had a body diode to absorb transients if the load is a relay. Continue reading RC PWM – ON/OFF switch
An upcoming project calls for a stand alone GPS logger.
The requirement is for a GPS stream that allows correction using RTKLIB, but this trial is of a lesser GPS as proof of concept.
Above, the equipment consists here of a Ublox NEO-6M based GPS module (~A$15 incl on eBay) at left, an Openlogger (~A$15 incl post on eBay) at right, and a 12V-5V converter (~A$7 from Hobbyking) at bottom. The latter is a 5A converter, way overkill, but it was on hand. The GPS module has a 3V regulator on board for the NEO-6M chip.
Continue reading Trial of prototype stand alone GPS logger
A drive test of the OpenLog logger collecting raw NMEA data in parallel with the TinyTrak (VHF) was conducted. To maximise the performance of APRS, a fill-in digi / iGate was run at my home. The tracker used a 65W transmitter with quarter wave vertical in the centre of the car roof.
Above is an overview of the APRS and OpenLog tracks. Click on the image for a scaleable / zoomable view in Google Maps. Continue reading OpenLog for TinyTrak – drive test
There are a host of factors that contribute to data loss in APRS, to name just some:
- non-standard / sub-standard / poorly configured digipeaters;
- defect ridden iGates that lose, duplicate and corrupt packets;
- poorly configured mobiles;
- network congestion and interference;
- unpredictable equipment failures;
- basic geographical coverage of the network; and
- dependence on the ionosphere for HF APRS.
This article describes an enhancement to the popular TinyTrak (and its clones) to also capture the GPS stream to an inexpensive local data logger.
The logger does not interfere with normal radio APRS, it coexists with it and creates a properly timestamped fine detail log of positions over a very long time, a log that can be post processed into a range of graphic / map and tabular reports.
The datalogger used in an OpenLog. It is a simple logger that writes data to a micro SD card, costs about $A12 (inc post) for the logger and about A$10 (inc post) for a 16GB Class 10 micro SD card. (A slower card could be used, but they aren’t much cheaper.)
Above, the OpenLog data logger.
Continue reading OpenLog for TinyTrak
This article describes an enhancement to the DIY USB password generator, a small USB HID keyboard device that types a password stored in EEPROM automatically when it is attached.
The implementation was on a Digispark ATTINY85 General Micro USB Development Board which was purchased on eBay for a few dollars. The board uses different pin connections to USB to the original. Continue reading DIY USB password generator – (USB PRC) enhanced #1