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
A range of inexpensive serial to Hitachi style LCD interfaces are becoming available.
This article describes the settings for one sold by eshoppingcity1 (and others) on eBay (about A$6 for 5 inc post at the time of writing but they are getting cheaper). It uses the Philips PCF8574T I2C expander chip which is supported by the user developed Arduino LCD Library V1.2.
Continue reading I2C – LCD interface – Type 2
The Slot.it CA20Z is Ford GT40 supplied as a ‘white’ kit which requires assembly and painting work.
Above is the part assembled bodies for a CA20Z and CS23B after painting with Vallejo 73.601 grey primer surfacer and two full coats of Tamiya X-6 acrylic gloss. The inexpensive Chinese airbrush pictured has been used for a few bodies, and worked very well.
The bright colour should be easy to see in dark parts of tracks. Continue reading Slot.it orange CA20Z build
Transmit performance of 2m hand held transceivers reported relative field strength measurements for some transceiver / antenna combinations.
This article documents a more careful measurement of the absolute field strength of one combination, and application of that knowledge to the other results.
Measurements of field strength were done with Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) and a small loop antenna.
Above, the RFPM1 RF power meter.
Above is the small loop used for field strength measurement. It is 2mm hard drawn round copper wire formed into a circle 185mm in circumference, and a common mode choke is used to connect the loop to the RFPM1 power sensor. The common mode choke is 0.6m of RG58C/U with 0.5m of ferrite sleeves over it and its loss is accounted for in the “Other Loss” item.
Continue reading Transmit performance of 2m hand held transceivers – absolute gain estimates
A poster sought advice of the forum experts about in service evaluation of the loss of some coax feed lines…
Has anyone tested old coax cable to see if the loss increased over time? I just tested two different coax cables at 146 Mhz with the use of a Bird Model 43 Wattmeter. Power measurements were taken at the input of each cable followed by the output. The load in both cases was a 146 Mhz Ground Plane.
The test results seem to show losses similar to new coax although Berk-Tek foam coax may have had a lower loss when new.
1. Berk-Tek 6211 RG-8X Ultra Flex Foam Coax – 68 feet
Measured 25 watts in and 11.7 watts out which represents a 3.3 db loss. …
Assuming that the stated measured power is in fact the indicated forward power on the Bird 43 directional wattmeter and given that the actual Zo of the line should be very close to the calibration impedance of the Bird (50+j0Ω), then the Matched Line Loss (MLL) is very close to 10*log(PfIn/PfOut)=10*log(25/11.7)=3.3db which is significantly above the expected 2.6dB for ‘ordinary’ RG-8/X and warrants re-measurement as it suggests that the cable might have degraded a little. In fact, the OP later reports 10.7W out for 25W in which is MLL of 3.7dB against spec of 2.6dB… a more convincing case for replacement! Continue reading An interesting case study – in service evaluation of coax loss
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.
The 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.
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.
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
You could squeeze all this into a cell formula if you wished to avoid using a VBA function.
Above is an example measurement run made with a 100k/3950 sensor (Indicated) and the corrected data in brown.
I have evaluated three different series of STC 8051 architecture MCUs, the STC89S52RC, STC15F104E, STC15F204EA.
English documentation is hard to find, and in some cases the translation from Chinese to English is poor and diagram annotations (eg flow charts) are still in Chinese. Continue reading An experience with STC 8051 microcontrollers
Fox flasher MkII described a LED driver for an animal deterrent using a Chinese 8051 architecture microcontroller, the STC15F104E.
Above, the schematic. A very simple circuit with just a handful of electronic components (one capacitor, two resistors, one LDR, one Polyswitch, 4 x LEDs and the MCU). Continue reading Fox flasher MkII #3
Yet another release of AIM software is available, 910A at the time of writing. I have downloaded and tested 8 versions this year, most have been wanting. Again, there is very little detail on what has changed and likely impact on historical measurments.
A quick set of measurements was made on my test inductor pictured above. Continue reading Accuracy of AIMuhf system – AIM910A vs several recent versions on a ferrite cored inductor
Two recent correspondents have discussed matching a quarter wave monopole with two variable caps.
Two capacitor shunt/series match
The matching scheme involves a shunt variable cap at the end of the coax feed line, and a series variable cap to the monopole base. The radials are of course connected to the feed line shield.
This type of matching scheme requires that the monopole feed point has sufficient +ve reactance, ie the monopole is longer than resonant. Lets assume the R component of feed point Z is 35Ω.
This scheme incorporates the simple shunt match, and the value of the shunt capacitor can be found knowing the R value to be matched to 50Ω.
Above is a Smith chart of a model of the match at 14MHz. The monopole has been lengthened to have 100Ω reactance along with 35Ω resistance. In this case a series cap of 148pF and shunt cap of 150pF are required. Continue reading Matching a quarter wave monopole with two variable caps