micro pic VW golf project. - Page 3 - Electronic Circuits Projects Diagrams Free

jay543_uk · 26th November 2007, 07:50 PM

woow, its gona take me a bit of time to work out how that circuit is working.So is that the sort of setup i would have to use on the sensor inputs so not to interfear with the signals goin back to my ecu.

im guessing that as the opamp should not be putting any load on the signal

thanks for all this help, its alot harder than i fault it would be but im learning alot from it and its even giving me more ideas for different projects.

i may have fault of one problem, The MAP sensor. The signal from this is gona be very messy because its measuring vacuum and pressure in the engine.when there is a vacuum in the engine its not constant as the pistons are goin up and down so i guess i could end up with a lot of voltage changes very quickly, high frequancy i guess. will this be a problem

jay543_uk · 26th November 2007, 08:51 PM

i maybe stupid but i dont understand what the 7660 is really doing, i get the voltage divider before the opamp and the resistors to adjust the gain but what the hell is the 7660, why is it only going to channel 0 opamp. is it coz both opamps are in one ic.

i think im missing something about opamps, i can under stand needing negative when using them with ac but why do you need negative on dc. maybe i should give up,doin my brain in.

HELP.

**Nigel Goodwin** · 26th November 2007, 09:02 PM

The 7660 gives a negative rail for the opamp - this is so it can swing fully to zero, opamps don't swing completely to either power rail (even so called 'rail-to-rail' ones) - by using the 7660 and a 2.5V reference voltage, it gives full and accurate swing from zero volts to maximum.

jay543_uk · 26th November 2007, 09:19 PM

how does the 7660 give out a negitive figure if its running on dc, negitive figures are only on ac. is the 2.5 ref on the pic ad3

can you make it any simplier or is that as simple as it gets.

iv just re read the basic electronics book iv got on opamps and it just talks about ac

going to run some times on a board and see what results i get

thanks for the help nigel, please dont give up on me just yet

**Nigel Goodwin** · 26th November 2007, 09:24 PM

Quote:

Originally Posted by jay543_uk

how does the 7660 give out a negitive figure if its running on dc, negitive figures are only on ac. is the 2.5 ref on the pic ad3

Essentially it changes the DC to AC, it's called a 'charge pump', the MAX232 works in a similar way.

Quote:

can you make it any simplier or is that as simple as it gets.

Pretty much as simple as it gets.

Quote:

iv just re read the basic electronics book iv got on opamps and it just talks about ac

opamps work on both.

jay543_uk · 26th November 2007, 10:35 PM

iv attached a circuit that i made from info in one of the last posts by picbits, iv not added any filters yet but is this the right sort of idea. i under stand that the opamp will never go above 3.2 volts so the pic is safe.

does it need a filter after it, ie resistors and caps.

regards jason

**Nigel Goodwin** · 26th November 2007, 10:39 PM

Quote:

Originally Posted by jay543_uk

iv attached a circuit that i made from info in one of the last posts by picbits, iv not added any filters yet but is this the right sort of idea. i under stand that the opamp will never go above 3.2 volts so the pic is safe.

Notice my circuit has a resistor from the opamp to the PIC, this keeps the PIC safe. Have a study of opamps, and then ask yourself why R4 is there?.

Quote:

does it need a filter after it, ie resistors and caps.

Before it would make more sense - you want to protect the opamp as well.

picbits · 27th November 2007, 10:46 AM

I only put the filter after the opamp so I interfere with the input signal as little as possible. Some of the crankshaft/camshaft sensors use a high frequency drive to them so I'm a little wary about putting any capacitance on thats side of the opamp.

In practice it probably wouldn't affect them too much but as I'm desigining stuff for use on customers cars I wouldn't want to take the chance.

**Nigel Goodwin** · 27th November 2007, 11:07 AM

Quote:

Originally Posted by picbits

I only put the filter after the opamp so I interfere with the input signal as little as possible. Some of the crankshaft/camshaft sensors use a high frequency drive to them so I'm a little wary about putting any capacitance on thats side of the opamp.

In practice it probably wouldn't affect them too much but as I'm desigining stuff for use on customers cars I wouldn't want to take the chance.

It wouldn't affect them at all, as it's after an attenuator.

You probably also need to re-eveluate your understanding of 'high frequency'

picbits · 27th November 2007, 11:54 AM

lol - my definition of high frequency is anything outside my audible range.

Actually my definition of high frequency is coming down as I get older lol.

picbits · 27th November 2007, 12:02 PM

Quote:

Originally Posted by Simtec 56.5 manual

CAS (Primary Trigger)
The CAS consists of a toothed disk and an two coils (exciter and modulator). The disk is attached to the crankshaft and
theoretically comprises 59 teeth set around its circumference. At a position 114° BTDC, one tooth is omitted as a reference to
TDC and so a total of 58 teeth remain on the disk. A high frequency signal of between 120 and 180 khz is delivered to the exciter
coil by the ECM.

There you go - even Siemens classifies it as a high frequency

**Nigel Goodwin** · 27th November 2007, 12:15 PM

High in the mechanical world, but low in the electronics world!

jay543_uk · 27th November 2007, 08:10 PM

Quote:

Notice my circuit has a resistor from the opamp to the PIC, this keeps the PIC safe. Have a study of opamps, and then ask yourself why R4 is there?.

when you say the resistor after the pic protects it, do you meen it stops the pic being damaged if the opamp shorts out.

as for R4 iv got no idea, these opamps are doing my brain in. i get how to use them as a follower or how to get gain from them but just not getting the negitive side of things.

surfing the net now to try and find things out

jay543_uk · 27th November 2007, 08:27 PM

do i need to worry about using the opamp to go negative like in nigels diagram or can i just use the same sort of layout i attached earlyer to one of my posts, but add filter

is the filter just to stop high frequancys being sent to the pic???

**Nigel Goodwin** · 27th November 2007, 08:31 PM

Quote:

Originally Posted by jay543_uk

do i need to worry about using the opamp to go negative like in nigels diagram or can i just use the same sort of layout i attached earlyer to one of my posts, but add filter

If your opamp is connected between 0V and 5V it can't go negative, because there's no negative voltage there. In my case the resistor from the opamp to the PIC protects it both ways.

Quote:

is the filter just to stop high frequancys being sent to the pic???

It's not just a filter, part of it should be (see nyquist frequency), but it needs to stop big nasty spikes as well.

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26th November 2007, 07:50 PM	(permalink)
jay543_uk	woow, its gona take me a bit of time to work out how that circuit is working.So is that the sort of setup i would have to use on the sensor inputs so not to interfear with the signals goin back to my ecu. im guessing that as the opamp should not be putting any load on the signal thanks for all this help, its alot harder than i fault it would be but im learning alot from it and its even giving me more ideas for different projects. i may have fault of one problem, The MAP sensor. The signal from this is gona be very messy because its measuring vacuum and pressure in the engine.when there is a vacuum in the engine its not constant as the pistons are goin up and down so i guess i could end up with a lot of voltage changes very quickly, high frequancy i guess. will this be a problem

26th November 2007, 08:51 PM	(permalink)
jay543_uk	i maybe stupid but i dont understand what the 7660 is really doing, i get the voltage divider before the opamp and the resistors to adjust the gain but what the hell is the 7660, why is it only going to channel 0 opamp. is it coz both opamps are in one ic. i think im missing something about opamps, i can under stand needing negative when using them with ac but why do you need negative on dc. maybe i should give up,doin my brain in. HELP.

26th November 2007, 09:02 PM	(permalink)
Nigel Goodwin	The 7660 gives a negative rail for the opamp - this is so it can swing fully to zero, opamps don't swing completely to either power rail (even so called 'rail-to-rail' ones) - by using the 7660 and a 2.5V reference voltage, it gives full and accurate swing from zero volts to maximum. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

26th November 2007, 09:19 PM	(permalink)
jay543_uk	how does the 7660 give out a negitive figure if its running on dc, negitive figures are only on ac. is the 2.5 ref on the pic ad3 can you make it any simplier or is that as simple as it gets. iv just re read the basic electronics book iv got on opamps and it just talks about ac going to run some times on a board and see what results i get thanks for the help nigel, please dont give up on me just yet

27th November 2007, 10:46 AM	(permalink)
picbits	I only put the filter after the opamp so I interfere with the input signal as little as possible. Some of the crankshaft/camshaft sensors use a high frequency drive to them so I'm a little wary about putting any capacitance on thats side of the opamp. In practice it probably wouldn't affect them too much but as I'm desigining stuff for use on customers cars I wouldn't want to take the chance.

27th November 2007, 11:54 AM	(permalink)
picbits	lol - my definition of high frequency is anything outside my audible range. Actually my definition of high frequency is coming down as I get older lol.

27th November 2007, 12:15 PM	(permalink)
Nigel Goodwin	High in the mechanical world, but low in the electronics world! __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

27th November 2007, 08:27 PM	(permalink)
jay543_uk	do i need to worry about using the opamp to go negative like in nigels diagram or can i just use the same sort of layout i attached earlyer to one of my posts, but add filter is the filter just to stop high frequancys being sent to the pic???