Me again.
posted it in the wrong folder.
Bought a small 9 V power supply, connected it to the sensors. The logomatic gets its voltage through a 5V regulator. Now the measurments are more stable, but still 35mV / 3.5 centigrade off. Seems the 3.3V voltage is a bit whacky. Can I supply the 3.3V externally? Shall I crank it up to 6V?
Cheers,
Steffen
Try stepping down the regulated 5v with one or two diodes (like IN914). Two should drop it down to about 3.3v
Try filtering the power supplies pins of both Logomatic and sensors with L-C filter, let say 10uH and 10uF.
Filter also the ADC inputs with R-C.
Where are your sensors located?
Angelo
P.S. Avoid opening a new thread each time you have a new question about the same subject: it is hard to understand your problem in a global manner.
reg new threads: thought its new topics so it may easier to find for the future reader.
reg. 3.3V: just about to chase up a LM1117T or something like that, bit tricky to find it in Australia.
two sensors are on veroboard, about 200mm wire to the logomatic. Put in another one via 3m cable, first it came up with random numbers. Then I tid it like in the LM35 datasheet, put 75ohm and 1µF from signal to ground, improved a fair bit, but still spikes every now and then. Actually, as soon as I touch the logomatic it comes up with funny readings, just put the last bit of two of its corners on a bit of plastic.
Oh dear, would have been easier and cheaper using ds18s20s…
http://i212.photobucket.com/albums/cc4/ … p5June.gif http://i212.photobucket.com/albums/cc4/ … temp-1.gifthe blue one is the one on a cable, the others sit on the veroboard
Sadly I believe the logomatic needs more internal work before it can properly function as an analog sensor reader. Using Vcc as Vref is just somewhat silly to begin with.
Polux rsv:
Try filtering the power supplies pins of both Logomatic and sensors with L-C filter, let say 10uH and 10uF.Filter also the ADC inputs with R-C.
got the parts Monday, but only today had time to solder. Works better it seems, will let it run all night…
Thanks!
Post your results about signal quality, noise, etc… Many people will be interested.
Angelo
seems it did not really hange. The one with the spikes is the one hanging on 3m cable, unshielded. At home, not really that harsh environment. At least the offset stays constant since I put the LM1117 3.3V in, before I hooked it up to 5V the offset was 8 today, 3 tomorrow…
Offset as in, have a thermometer, can compare if the thermometer says 22° and calulations for the sensors next to it yield say 16°…
http://i212.photobucket.com/albums/cc4/ … 25June.gifwhats the deal with digital logging, can I log say once per minute and hook up BS18s20s?
edit, ok, scrolling up and down, looks a bit (not a byte :roll: ) better. Maybe put a bigger capacitor in? The LM1117 does a wobbely 3.3 V as well, the multimeter was a bit nervous…
the 2 parallel curves “ins top” and “living floor” is the ones where I plugged the sensors in. The graph is without the averaging I’d normally use. The 17.5m CAT5 does better than even the “subfloor” which is about 2m normal cable.
I connected 1 pair to voltage supply and ground the other pair to sensor output and same ground (i.e. ground would be 2 strains). The other option may be one pair for the sensor output so in that pair the noise would neutralise. But, seems to work for me the way it is now and the spec says one pair would be signal and its ground, that’s how I did it.
This is interesting to me. I am logging voltages up to 5V with a divider and have not seem much of a temperature effect . The specs on the regulator are also pretty tight according to the data sheet (2 0ppm/degree C or so- i can’t remember but it was not bad). I am averaging many readings and do have an RC filter on the input.
