First project practically complete - "black box" logger

[GreenLeader]

Well I am pleased to say that I have practically completed my first proper picaxe project. It took about a year but I have built and tested the prototype. I got a lot of help from this forum, either browsing posts or from vey helpful answers to my questions. Still a few bugs to sort out, but in the main its working well.

It's a 7 channel logger for my car - a bit like a black box recorder.

It all started because I wanted to verify the turbo boost pressure - the dashboard gauge has graduations, but no numerical markings, so its hard to tell if you could be over-boosting. Then it grew into other things.

So I ended up with a 40X1 logger with 3 "high speed" channels (up 10 Hz each) and 4 slave channels running at 1/5th of the masters. Master sample rate selectable by switches on the panel.

Masters are engine rpm, boost pressure and road speed.
Slaves are ambient temperature, intake temperature and two spares (plan to use them for oil temperature and pressure later on).

It has 2 modes - streaming and standalone. In standalone it automatically starts logging when powered up (when you start the car). It writes to EEPROMs, enough to record at 10Hz for 54 minutes, but at the lowest rate (1Hz) you get about 9 hours. Has a circular mode to keep only latest data if preferred. Upload speed is a bit slow - takes about an hour at 115200baud.

In streaming mode it can stream continuously to a connected PC running a terminal program to collect data indefinitely (about 9-10Hz on all channels)

Has a 4x20LCD to give the user some feedback about what's going on..

Attached a is graph of a typical recording and a photo of the logger..

 

[westaust55]

"black box" logger

Looks and sounds pretty darn good GreenLeader.

Any schematics or software going to be posted for future edification as well ?

 

[GreenLeader]

Thanks...
The code is probably too long to post - I am not the best programmer so it just about fills the available picaxe space. There are about 10 pages of schematics. If there are specific points of interest I could post the relevant parts though...

 

[rbright]

Come on Green Leader....

Would it be more practical to just pdf the schematics & code to publish.
PS I'm enjoying your FreeBasic Analog logging Post on the other topic. Interesting how many Westralians are on this forum.
Cheers

 

[Andrew Cowan]

Are you using DS18B20s to measure the temperature?

A

 

[GreenLeader]

I am using LM35's or LM61's for my temperature sensors. So with 10bit ADC resolution you have about 0.5 degree C resolution - good enough for me.

As long as the leads are less than about 1.5m long, they seem to work well. Anything longer and they get noisy (completely unusable). You can use capacitors to filter the noise out, but in my application I have just kept the leads short.

 

[GreenLeader]

Would it be more practical to just pdf the schematics & code to publish.
PS I'm enjoying your FreeBasic Analog logging Post on the other topic. Interesting how many Westralians are on this forum.
Cheers

Many thanks for the feedback... Yes there are a few of us WA (AU) folks around....

I am still debating whether I would release the project in its entirety. On the one hand it would be nice to order a batch of boards and assemble and sell a few units to get some emotional (and perhaps only notional) return on my "investment".

On the other hand that might be more hassle than its worth....

I'm interested to hear what others have done with their projects - one-off's for own use? Or has anyone managed to sell a few.

Still got a lot to do to make a usable FreeBasic application to collect/graph the streaming data off my logger. At my rate of progress it might be another year!! But I certainly can see the huge kick start and time saving you can get when someone posts a good example that you can learn from...

 

[lbenson]

Could you provide your code for the LM61--it wasn't clear to me from the datasheet how to calculate the temperature, tho it showed how to calibrate it for an alarm.

 

[GreenLeader]

LM61

Partial code to read an LM61 connected to ADC input 3 on 40X1.
Output is 10mV per degree C, with 0 degrees sitting at 600mV (which looks like 60 degrees C)...

symbol Ta    = w4        ' Ambient air temperature     b8,b9          0/100
readadc10 3,Ta
Ta = Ta * 49/100 - 60    'degree C (LM61 has 60 deg C offset)

' or you can have it in 1/100th of a degree
'Ta = Ta * 49 - 6000      ' temp in hundredths of deg C (LM61 has 60 deg offset)

 

[lbenson]

Thanks. I'm sure it was there, but I missed the "Output is 10mV per degree C, with 0 degrees sitting at 600mV". Since I need a dozen+ temp sensors, the LM61 will save me some $$ relative to the DS18B20.

 

[GreenLeader]

Yes they are very cheap - but accuracy is not so good: +/- 2 or 3 degrees C.