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31  Using Arduino / Project Guidance / Re: Vehicular emissions sensors ? on: September 26, 2014, 07:15:45 pm
I've been around Sun testers since c1969: the ones my family use/d all have air/'fuel meters. Admittedly back in the day the mechanic had more access to adjustments (screws on carbs, jet sizes, float height, all sorts of stuff) to keep the ratio at the stochiometrically correct 14.7- not much to do nowadays except maybe shake the shit out of the aircleaner element and change the plugs.
So the lambda reading I got in July, for my old car, of 1.015 (on a Sun DGA 2500 MOT) means it was 1.5% above that 14.7 ratio? 14.7 * 1.015 = 14.9205. Not bad for a 15 year old car.
32  Community / Bar Sport / Re: Coming soon..... on: September 23, 2014, 10:46:19 pm
.... to a supplier near you.
Seen them on Ebay at £1.86 (from China), free P&P. How does that compare with 225 Rand?
33  Community / Bar Sport / Re: Lead free solder on: September 23, 2014, 10:33:05 pm
The variables are too chaotic to nail down with any certainty.
Especially if you're using lead nails.  smiley
34  Using Arduino / General Electronics / Re: Help with small electronics project on: September 23, 2014, 09:08:48 pm
How are you controlling the motor?
35  Using Arduino / Programming Questions / Re: Getting code from serial data on: September 23, 2014, 08:57:33 pm
Maybe I'm not seeing this correctly but my approach would be to check each character as it comes in. If it matches the first character I'm looking for then check the next character matches my second character, etc., etc.  If you're only looking for a matching part of the string, why do you need a buffer? You would only need a buffer if you need the whole string after you've found the match in it or are trying to match several different things. I'm thinking something like this:
If (inputCharacter== "H"){ //look at next char input
    if (inputCharacter =="E"){//look at next char input
          if (inputCharacter =="L"){//look at next char input
                 if (inputCharacter =="L"){//look at next char input
                       if (inputCharacter =="O"){
                            //string "HELLO" found. No need to check remainder of input.
                               do your stuff;
else if(inputCharacter ==NUL) {
Serial.println ("String HELLO not found")
36  Using Arduino / Project Guidance / Re: Hygrometer Sensor Problems on: September 23, 2014, 07:11:17 pm
Hello and thank you all for your answers.

First of all my shield is for moisture or something else? The description was "Soil Moisture Sensor Soil Hygrometer Detection Module For Arduino".
Yes. It's for measuring the moisture in soil, not air.  It does that by measuring the resistance between the two metal prongs. It's has both analog and digital outputs. AO & DO.
37  Using Arduino / Project Guidance / Re: PSTN/MODEM IC - Talk over Phone Line on: September 23, 2014, 07:02:28 pm
See this thread:
38  Using Arduino / Project Guidance / Re: Vehicular emissions sensors ? on: September 23, 2014, 06:45:46 pm
All emissions equipment uses a sniffer and a pump to sample the exhaust.

Cool exhaust is sucked into the machine, i have never met an emissions station that reads Lambda {air fuel ratio}
All the ones used for MOT testing in the UK measure Lambda. They have to, by law.
Lamda correlates to a cars performance, but not to its emissions, specifically.
If you know the NOX the lambda is irrelevant.
And vice versa. UK exhaust testers do not measure NOX, only CO, Hydrocarbons and Lambda.
39  Using Arduino / General Electronics / Re: Momentary dip switch? on: September 22, 2014, 11:36:56 pm
They could be 2 bays wide: 4 buttons in an dil-8 length, would be very handy.
Maybe some very small microswitches, like those used in a mouse, would work?
40  Using Arduino / General Electronics / Re: 12v input to 7805 voltage regulator heating in a second?? on: September 22, 2014, 11:12:26 pm
For a TO220 device something like 0.5W is the maximum you'd really want to
put into it without some sort of heatsinking.   If you have 12V supply to a 7805
that's suppling 70mA you will be at 0.5W dissipation already.

If you put 1.5A through it the dissipation will be 1.5 x 7 = 10.5W and a medium
sized heatsink and a fan would be required (or a large heatsink).

A DC-DC converter would waste much less power and run at a sensible temperature
without such issues....
Or you could use a L78S05 (rated at 2A max), but you'd still need a heat sink.
41  Using Arduino / Programming Questions / Re: Avoiding Delay (blinkwithoutdelay) help on: September 22, 2014, 11:04:54 pm
I may be wrong, but I seem to remember reading that the microseconds counter is only updated every 4 micros. How then, can there be a measured 5 microsecond delay?

Good point, he can't smiley-wink
Its probably going to return either 4 or 8 depending on the system overhead.
I can't see it returning 4 if he's asking for a 5 micros delay.
I cant stress enough, that for something on this order of magnitude an interrupt would be better suited.
One of the rare cases where an interrupt is required.
42  Using Arduino / Programming Questions / Another timing answer on: September 22, 2014, 10:46:06 pm
As suggested by AWOL, above...Blink without delay, or
43  Using Arduino / Project Guidance / Re: Vehicular emissions sensors ? on: September 22, 2014, 10:06:24 pm
Thank you, for the responses !

Exhaust gasses, once they have passed through the silencer, possibly the catalytic converter and the rest of the exhaust system are not very hot, usually not above about 50°C.

That seems to be my concern. For example, this datasheet for CO sensor - MQ-7 - reports the operating temperature limit as -20°C to 50°C. Wouldn't that be cutting too close ?
Not if you do as I suggested above: "use a length of exposed (to cool air) metal tubing to take the gasses from the tail pipe, any excess heat will be dissipated by the time the gasses reach your sensors. "
I think that about 6 ft (2 Mtrs) would be sufficient, depending on the airflow and temperature around it. The tubing doesn't have to be straight!
44  Using Arduino / Project Guidance / Re: Coding help required on: September 22, 2014, 09:54:11 pm
You've posted your code (incorrectly) but haven't told us what the problem is.
There's no need to make another post to correct something, just modify (edit) your original post.
45  Using Arduino / Project Guidance / Re: Hygrometer Sensor Problems on: September 22, 2014, 08:14:05 pm
hello i am trying to make a simple project and get a value of the hydrogene in my room. It keeps returning 0...anyone knows why? :/I use D0 digital pins actually pin 3
You are trying to digitalRead an OUTPUT. It doesn't work, as you've found out.  Try digitalReading an INPUT.
An hygrometer measures the Specific Gravity of a liquid and has nothing to do with hydrogen gas.
If you've hydrogen gas in your bedroom, I hope you don't smoke.  smiley-eek
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