Mini60 antenna analyser

There seems a never ending stream of low end antenna analysers appearing.

The Mini60 antenna analyser is one in that vein, and is sure to prove popular because of its low price. As is common, there does not appear to be an English language user manual and the specifications in eBay ads are not very reliable (eg weight: 200kg).

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Above is a screenshot from an online demo of the Mini60 on a 7MHz antenna. Continue reading Mini60 antenna analyser

USBTiny

I bought a USBTiny AVR programmer on eBay for about A$8 posted.

HOT NEW Usbtinyisp AVR ISP Programmer FOR Arduino Bootloader MEAG2560 UNO R3 | eBay - Mozilla Firefox firefox 06/08/2015 , 08:24:12

 

Above, the seller’s pic of the package.

It is almost always the case that the ISP headers on the programmer use the standard pinout published by Atmel, and in that case the supplied ISP cables need to be pinned pin for pin, ie pin 1 to pin 1 etc.

If you look carefully at the pic, the key is towards the top of the pic which means pin 1 on the right hand plug is towards the viewer and pin 1 on the left hand plug is away from the viewer. The cable does not connect pin 1 to pin 1, and as a consequence the package did not work.

6wayDil

There is more than one way to connect these plugs, and above is one way that does connect pin 1 to pin 1, and the cable and USBTiny work. Though the seller has been told of this defect, he continues to sell the item with the pic of the defective cable.

One wonders how many thousands of these things are and will be sold with this defect.

 

A tale of two USB-RS232 adapters

There are a number of USB-RS232 adapters available, among them Silabs, FTDI, Prolific and WCH.

The Silabs CP series adapters have been reliable but not very widely used.

The Prolific adapters are, well, prolific… but given their major compatibility problems and poisoned drivers, they are not a good choice.

FTDI was a good choice until they distributed through Microsoft Windows Update their device poisoning trick to disable chips they thought counterfeit… though they seemed to have backed away from that action.

The new kid on the block is an adapter by Chinese company WCH, chips that appearing in lots of low cost devices, eg Arduino Nano clones with WCH adapters instead of FTDI selling for around A$3+ on eBay whereas the FTDI equipped Nanos are more like A$12.

This article compares the WCH  CH340G and  FTDI FT232RL.

2USBRS232Above are two inexpensive adapters for Arduino boards, the upper one is FTDI based at A$8 each (inc post), and the lower one WCH based at 3 for $3.60 (inc post). Continue reading A tale of two USB-RS232 adapters

Solar power supply for foxflasher2

The Fox flasher MkII is designed to run directly from a 1S LiPo battery at 3.8-4.3V. The battery can be charged by a simple voltage limited charger to 4.1V with a small loss in capacity. This article describes a simple solar charger for such a battery.

The regulator uses a TL431 precision programmable reference in a simple shunt regulator.

PV6V1W

Above, the 6V 1W PV array. Continue reading Solar power supply for foxflasher2

Arduino HMC5883 magnetometer – a tutorial

This tutorial shows how to explore an inexpensive HMC5883 3 axis magnetometer module with Arduino.

The magnetometer module can be purchased on eBay at very low cost (<$3), and is an ideal educational project for the budding Arduino practitioner.

It is an ideal low cost project for a first exploration of explore I2C, and the basis for a digital compass. This particular module breaks out DRDY which is useful for interrupt driven applications.

Fig 1
Fig 1

Fig 1 shows the test setup:

  • at the top is a Arduino Pro 328 with Opti bootloader and FTDI adapter for programming;
  • middle is the HMC5883L module; and
  • bottom is a Logic Shrimp for logic tracing.

Continue reading Arduino HMC5883 magnetometer – a tutorial

Arduino stepper motor – a tutorial

This tutorial shows how to explore an inexpensive stepper motor and driver board using an Arduino and included stepper library.

The stepper motor and driver board can be purchased on eBay at very low cost, and is an ideal educational project for the budding Arduino practitioner.

Fig01
Fig 1

Fig 1 shows the test setup:

  • at the top is a Arduino Pro 328 with Opti bootloader and FTDI adapter for programming;
  • middle is a Logic Shrimp for logic tracing;
  • bottom left is a 28BYJ-48 stepper motor; and
  • bottom right is a driver module based on UNL2003.

Continue reading Arduino stepper motor – a tutorial

Arduino thermistor thermometer – a tutorial

This project was designed ad-hoc as a learning exercise for a friend who ‘needed’ to acquaint himself with Arduino.

What better than a practical exercise that demonstrates some key advantages and disadvantages of the Arduino environment.

The project was a simple digital thermometer to display normal environment air temperature, say from -20° to 50° using common and inexpensive Arduino hardware with firmware developed on the free Arduino IDE, all using hardware that was on hand. Continue reading Arduino thermistor thermometer – a tutorial

RC4 thermistor characterisation.

I have a little RC-4 temperature logger which has been a really handy device for ensuring that our freezers are cold enough, but no colder.

RC-4The RC4 has an internal sensor and is supplied with an external sensor that plugs into a 2.5mm TS jack on the side.

This article explores an alternative sensor that could be embedded in equipment of interest. The sensor is a NTC thermistor.

Firstly, I found that none of the 2.5mm TS plugs I had connected to the RC4 properly, but the T-R of a TRS plug worked reliably.

The display was observed with two 0.1% precision resistors and the thermistor characterised.

Screenshot - 07_07_2015 , 12_25_20

Above, it looks like nominally a 110k/B=4200 thermistor… which is a little unusual. 100k thermistors with B=3950 and 4200 are fairly easy to obtain though.

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Above is a chart of the error in using the two commonly available thermistors. At low temperatures the 100k/4200 isn’t too bad, around 60° the 100k/3950 is better.

It is a simple matter in Excel to correct readings made with a different thermistor. Here is a VBA function to perform the conversion.

Function temp2temp(ft, ft0, fr0, fb, tt0, tr0, tb)
'function to correct temperature reading to a different thermistor
r = Exp((1 / (ft + 273.15) - 1 / (ft0 + 273.15)) * fb) * fr0
temp2temp = 1 / (1 / (tt0 + 273.15) + Log(r / tr0) / tb) - 273.15
End Function

You could squeeze all this into a cell formula if you wished to avoid using a VBA function.

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Above is an example measurement run made with a 100k/3950 sensor (Indicated) and the corrected data in brown.