New to electronics - Soldering

[Paul_B]

Afternoon all,

I never did electronics at school and although I'm quite happy with the concepts, physics and maths the practical side is a bit more daunting. However, I'll give anything a go once.

My latest project is to use temperature sensors (I believe correct terminology is thermistor) at various levels of my new thermal store to report into Cortex. Chris came up with the component on a previous thread and Karam told we what I needed to do

ATC Semitec IP67 10K Precision NTC Thermistor Probe with Lead
"...regards the thermistors what you will need is a set of 'pull down' resistors i.e. so that you form a potential divider for each sensor at the QAI input (sensor connects between 3.3V terminal and channel input and resistor connects between channel input and 0V terminal)..."

looking at the QAI reference doc I believe the schematic of the above is as follows:
QAI.jpg
Source: QAI Datasheet from Idratek website

But turning the advice and schematic to physical connections I'm a bit unsure. So whilst practicing the soldering I did two versions:

Two wires from resistor twisted together and soldered on to the resistor:
WireTogetherandResistor.jpg

Second option is separate the wires and connect to the resistor:
WireSeperateandResistor.jpg

In my mind both achieve the same but I wanted to check with those who have more experience.

Paul

[toscal]

While both are ok, go for the first option as its one solder joint.

[Karam]

I don't know where these wires are going but my initial thoughts would be just to cut the 'pull down' resistor wires to a suitable length (if needs be), preferably insulating bare bits with a bit of sleeving (can be obtained by stripping a spare bit of suitable gauge wire) and screw directly into the terminal blocks (connecting between the relevant channel terminal and a 0V terminal). Then the only remaining wires will be those coming from the thermistor/s. For these it might be convenient to use a twisted pair within a CAT5 cable - particularly for example if the thermistors are in a little bit of a group at a distance from the QAI. Anyhow these wires can then also be screwed into the terminal blocks (between the relevant channel terminal and a 3.3V terminal). I think you should be able to fit two wires into each terminal so maybe it can all be done with no soldering, other than perhaps between the thermistor and the CAT5 twisted pair.

[chris_j_hunter]

IIRC, we used twisted pairs in Cat-5e between sensor & module (typically a few metres), and ran the wire ends & the resistor wires straight into the terminal blocks, with cutting, but without any soldering - each screw terminal will take a few wires, small hands & fingers helpful !

BTW: for where we have had to solder, we bought a temperature-control soldering iron - much much better than an uncontrolled one, we found (like this, but don't recall it being quite so expensive) :

http://www.rapidonline.com/Tools-Equipment/Weller-WSM-1-WSM-1C-soldering-stations-300663

and some heat shrink sleeving (used with hot-air gun) - lots to choose-from here :

http://www.rapidonline.com/SearchResults.aspx?kw=heat+shrink&srb=0&dir=0&cat=6422

PS: for joining sensor wires to Cat-5e strands, we used this sort of thing :

http://uk.rs-online.com/web/p/push-wire-terminals/5104775/

quick & easy & reliable ...

[Paul_B]

Chris,

I ended up completing the task with solder. Time will tell concerning the quality of my work.

Your description of what you used and where is very similar to what I did. I too invested in a new soldering iron work station but went with the cheaper 40W Weller analogue station. I found it pretty easy to use once I got the hang of it, the temperature set correctly, tinning the tip and a few videos on YouTube of what I was trying to achieve. I also covered the work with heat shrink sleeving to protect the wire, solder and resistor.

Thanks

Paul

[Paul_B]

Looks like it all worked out well in the end. I now have four sensors reporting in via a QAI to measure the temperature at four heights of my new thermal store.

TopTemp.jpgFourTemps.jpg