Most items required for construction of this apparatus are inexpensive and easily obtained (RS Components supplied the vast majority). However a few items are expensive and it is worthwhile to try to reduce the costs of these.
Clearly the computer will be the main cost but in most situations one will already be available - e.g. to read this site! However for mobile application a simple (e.g. second hand) tablet or laptop would be appropriate, a fancy one is not required, although it is useful if it has Office for analysis of results.
As mentioned in the text of the site the apparatus can be powered effectively with a laptop power supply for 6-8 hours, so it could be powered for a shorter period using the batteries of the attached laptop.
A tablet would need a separate power supply e.g. a motorcycle or car battery. The battery needs to have a central voltage tap so the the dual rail power supply can be configured. Alternatively the apparatus can be run from a single rail power supply, although I have not tested this in any detail.
It is unfortunate that a mobile phone cannot be used at present but I have been unable to find one that works with (or contains) an A/D converter & has software for display etc. There is perhaps a niche market there!
The Dr DAQ converter I have used is superb, in that it performs so many useful functions both for use of the kit and for electronic design The software is easy to use & comprehensive, with very good graphics.
However at ca. £90 it is expensive & may render the apparatus uneconomic for some users. Thus I have tried to find an alternative, without success so far. It seems that 12-bit (or maybe 10) conversion is required to allow exploitation of the sensitivity of the kit, so that alone seems to rule out inexpensive converters.
Also the software & graphics seems often to be very poor,which means that the data must be transferred to Excel, which in turn requires the computer to be loaded with Office, which is quite expensive.
This area needs more research & I would appreciate any feedback any reader could give.
I tested an 8-bit converter purchased from Vellemann at £24 for the kit form, which took about 2h to assemble. This was usable for voltage changes of 100 mV & above but unsuitable for sensitive measurements owing to the 8-bit conversion.
The graphics were poor, so that it was difficult to see in real time whether a given measurement was working properly. It does however record data effectively at the 8-bit level, even if one cannot observe what is happening easily!
The heatsink cost £12 but could be home-made.
The two SN2055 power transistors can be replaced with a single Darlington transistor (TIP122) but the heatsink needs to remain approximately the same size.
I am currently working on a TEC cooling sytem for hot climates & will report on this in due course.
The apparatus would greatly benefit from being implemented on a well-designed single printed circuit board & used free software to design a board & then get it made commercially. My first attempt at this was not successful - I put some of the tracks too close to each other & this resulted in cross-talk.
I need to try again!
Circulating FAN. This 40 x 40 mm 1W, 12 volt fan (ebmpapst) cost £12 and is quite powerful, any reduction in power is likely to affect the thermostat performance.
Some aspects of costing
Suggestions for economies
Alternative components that can be used