Urgent help Required - Condition Signal

[Pommie]

If you can get your signals consistent at 0 and -14V then connect the -14 to pic ground and use a voltage divider on the 0V signal. Or do you need the ground lines connected?

Mike.

 

[MikeMl]

If you can get your signals consistent at 0 and -14V then connect the -14 to pic ground and use a voltage divider on the 0V signal. Or do you need the ground lines connected?

Mike.

There is no -14V! It is +14V (battery positive if car is running, likely 12.6V if car is not running)

 

[Huttojb1]

There is no -14V! It is +14V (battery positive if car is running, likely 12.6V if car is not running)

I agree, there's something weird going on. I'll try tomorrow as suggested and post back on here.

I'm sure when I monitor these signals previously I had a positive voltage, maybe I was running the scope on the battery!!!

Jason

 

[Huttojb1]

Ok. New update.

Running the scope on battery I get my desired positive voltage. For my understanding, what's the reason behind this?

The attach is still signal A in reference to Signal B.

I'm gonna see both signals in reference to ground. And post back.

Jason.

 

[Huttojb1]

This is now more like it......

Signal A channel 1
1.2 sec System power Up
1.5 sec ignition on
2.4 sec 1st gear selected
3.3 sec neutral selected

Signal B - Channel 2

So am I correct in saying, I can ignore Signal B. Use Signal A to my ADC of my PIC (with relevant drop down, protection and smoothing) and I'll be able to read this voltage.

Would my PIC do the same as what the scope was doing when it was on the mains power? Do I still need to put a resistor across SigA and SigB?

Jason.

 

[alec_t]

I am sure everyone here assumed you mean the negative signal wzs with reference to ground which is 0 volts.

That was my understanding too.

 

[MikeMl]

Since the signal you are interested in has only two "levels", why run it into the ADC? Just clean it up (lpf or Schmitt), and run it into a normal port pin and treat it as a 1 or 0.

A "floating" scope can give some strange effects, as you found out. A scope operated from the AC line is usually grounded (earthed?) through the third wire (green) in the AC power cord. A car parked on a cement slab will be weakly earthed through the carbon in its tires. The rule is always to connect the ground clip of the scope to the frame of the car when probing around in a car.

 

[schmitt trigger]

What sort of automotive module are these signals coming from?
For the last 20 years I've worked for companies that build electronic assemblies for automotive, motorcycle and heavy machinery OEMs.

I've never seen a sensor, module, switch assembly, peripheral or anything remotely electronic, which outputs a negative voltage as a control or communication signal.

In this environment, one finds four broad signal types:
1) On/Off signals. Older vehicles had a mix between 0-5v and 0-vbat (either 12 or 24 volt) levels, but most modern vehicles have standardized towards 0-5v levels.
2) Analog signals. Again, on some older vehicles you may find 0-vbat, but things are standardizing towards the 0-5v level.
3) PWM signals. These are exclusively 0-5v levels, unless it is a power PWM which is driving lights or motors.
4) Serial bus. On these, the CANBus reigns supreme, which is a differential bus. Google it for info on its logic levels and termination requirements. I've also seen RS485 and LIN usage, but for very limited networks.

Everything is always referred to the vehicle's chassis, even though a separate negative return line is customarily employed.

With the exception of serial buses (which carry its own set of error and fault correction) what one sees in this environment, specifically for vehicle-critical signals, is redundancy in the form of a complementary signal.
For instance if you have a switch, it will be NO/NC configuration, and both signals are required to complete the action.

 

[Huttojb1]

For the last 20 years I've worked for companies that build electronic assemblies for automotive, motorcycle and heavy machinery OEMs.

I also used to work in automotive (TRW Automotive), I worked in the Electric Power Assisted Steering Division. I worked there for 10 years, I now work in aerospace now and have been for the last 6 years.

In this environment, one finds four broad signal types:
1) On/Off signals. Older vehicles had a mix between 0-5v and 0-vbat (either 12 or 24 volt) levels, but most modern vehicles have standardized towards 0-5v levels.
2) Analog signals. Again, on some older vehicles you may find 0-vbat, but things are standardizing towards the 0-5v level.
3) PWM signals. These are exclusively 0-5v levels, unless it is a power PWM which is driving lights or motors.
4) Serial bus. On these, the CANBus reigns supreme, which is a differential bus. Google it for info on its logic levels and termination requirements. I've also seen RS485 and LIN usage, but for very limited networks.

To be far, the Electric Steering Component was very advance using all the signals described above. I used to do Dealer Vehicle Visits so were very confortable with the CANbus on the vehicle. We started looking at LIN as the next Generation but CANbus was my confort zone. Although I understand the signals above and understand the use I struggle with fundermentles of electronics.

What sort of automotive module are these signals coming from?

The signal I have been describing is from a Motorcycle engine CBR1000F. (Look at my Profile Picture - it's fitted to that beast) I totally agree, I didn't expect to see negative voltage but as decribed above it seemed to be a scope grounding issue.
I beleive the signal is from the original motorcycle wiring loom where the signal use to drive a indicator on the original motorcycle dash to indicate Neterual has been selected.

Since the signal you are interested in has only two "levels", why run it into the ADC? Just clean it up (lpf or Schmitt), and run it into a normal port pin and treat it as a 1 or 0.

Thanks Mike. I could do but I'm still not entirely convinced that it doesn't change for other gears. I can only select 1st at the moment so going to use the signal going into an ADC and the output the ADC value whilst driving to finally fine out.

thanks for all your help.

Jason

 

[MikeMl]

... I could do but I'm still not entirely convinced that it doesn't change for other gears. I can only select 1st at the moment so going to use the signal going into an ADC and the output the ADC value whilst driving to finally fine out...

In that case, I would make the signal ratiometric with respect to the 14V signal. It is likely why they make it available on that other wire. That way, the ADC reading of the gearshift voltage would be independent of RPM (alternator spun up or not)

 

[Huttojb1]

In that case, I would make the signal ratiometric with respect to the 14V signal. It is likely why they make it available on that other wire.

Could you please explain further?

Jason

 

[Huttojb1]

Gents,

Update. See Movie!! Whoop woo.

Thanks everyone for your help.

Jason