DIY_EFI Digest Sunday, March 26 2000 Volume 05 : Number 123 In this issue: Re: Cheap protection... Re: Cheap protection... Re: Cheap protection... RE: MAP sensing for IR systems Re: Cheap protection... Re: Cheap protection... Re: Cheap protection... Re: Cheap protection... Re: Cheap protection... See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Sun, 26 Mar 100 17:59:44 +0800 (WST) From: Bernd Felsche Subject: Re: Cheap protection... Buchholz, Steven writes: >> Cost is a significant factor - the uC is worth only a few bucks, so >> I don't want to spend hundreds protecting it! Opto-couplers are a >> bit OTT (IMHO) and large. >> >> So far, a simple voltage divider with forward signal diode, and >> filter capacitor feeding into a (hex) Schmitt trigger (74C14) is how >> far I've got. But the voltage can vary from about 8V to perhaps in >> excess of 16V, but I want those levels to be "true" always. The >> Schmitt will sense 3.5 to 5V as true when running at 5V. >> >> Should I include a (4.7V) Zener on the input to the trigger? >... I forget the actual numbers, but not too long ago I was surprised to >read that blowing the horn puts spikes that can be somewhere in the 200v >region on the power lines ... I hope it's not that bad when you get further up the wire because most OEM ECU's would have trouble coping with much more than 80V. Maybe short spikes - they can be absorbed by capcitors. >I don't think the problem is the cost of replacing the CPU ... it is more >the hassle of having to fix something that's broken. That as much as anything - though designs I've seen (which isn't that great a number) have "sacrificial" components such as small-signal diodes, etc which will blow if somebody does the unthinkable and shorts a plug lead to a sensor input. Or something equally dumb. >I've seen optocouplers that come in small SMT packages ... I'll bet the cost >isn't that much. AAMOF, I picked up a really cool demo kit from >http://www.lumex.com that included optocouplers and a whole selection of >lamps, LEDs & displays. SMT is a bit of a rude word in my vocabulary. I'm not equipped for it at all. My hands are too shaky for normal soldering as is. The *count* of the parts is important, as is the cost. >It isn't clear to me that you need to have a voltage divider to protect the >input ... a series resistor, perhaps with diodes to the rails should be >sufficient. Some parts already have the diodes built in. I'd also put I don't think the 74C14 Schmitt trigger would like 12V input if it's running from a 5V supply rail. The Schmitt trigger connects to the inputs of the uC, which shares the regulated 5V supply. So I divide the external voltages on 2.2 and 1.2 MOhm resistors. That means I can cope with a nominal 9.9 to 14.2V range within the trigger levels (plus the signal diode drop). >ferrite bead filters on the signal inputs. You may want to look around to >see if someone doesn't offer an input device that has built-in protection. The protection capacitor doubles as a low-pass filter. The signals I'm sensing originate from switch closures and relay contacts in the main. So I can happily discard everything below a couple of kHz. The beads are a good idea, especially if the device were for something more significant than a "smart" courtesy light delay! The devices I'm planning to use already have "protection", but I like the belt and braces approach. The Schmitt trigger is the second-level sacrifice. Cheap to replace and easy to test. BTW: I discovered that leaving my GSM phone in the car sets of the car alarm. I was already swearing at the alarm when I noticed the phone clipped adjacent to the main wiring panel. Doh! So at least I have one way of testing anything I build against severe EMI. - -- Real Name: Bernd Felsche Email: nospam.bernie@xxx.au http://www.perth.dialix.com.au/~bernie - Private HP - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ Date: Sun, 26 Mar 2000 19:42:15 +1000 From: Peter Gargano Subject: Re: Cheap protection... ASCII art? Perhaps you should compose using a fixed font, say Courier, etc. - this looks just like a lot of scribble to me, and I'm sure you put a lot of effort into it too!... Mike Blakey wrote: > > --+--- +5v > l > l > ------- > / \ > /__\ 1N4148 > l > l > +---------+ l > 12v source >-----l 13k l---+------------> input > input +---------+ l to uP > l > l > +-----+ > l l > l 10k l > l l > +-----+ > l > l > l > --+----- GND > > - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ Date: Sun, 26 Mar 100 18:25:07 +0800 (WST) From: Bernd Felsche Subject: Re: Cheap protection... Mike writes: >At 11:28 AM 26/3/2000 +0800, you wrote: >>Cost is a significant factor - the uC is worth only a few bucks, so >>I don't want to spend hundreds protecting it! Opto-couplers are a >>bit OTT (IMHO) and large. >Yeah true - cost is a bummer and yes Opto's shouldn't be necessary due >to common ground (provided its a 'good' ground). >>So far, a simple voltage divider with forward signal diode, and >>filter capacitor feeding into a (hex) Schmitt trigger (74C14) is how >>far I've got. But the voltage can vary from about 8V to perhaps in >>excess of 16V, but I want those levels to be "true" always. The >>Schmitt will sense 3.5 to 5V as true when running at 5V. >Well, another option is to use a protected MAX232 RS-232 input/output >chip, this already has lots of ESD protection and overvoltage too, That's novel. A bit pricey though. Works out about twice the cost per input as opto. I was aiming at $20 in parts for the lot (well, about $25 including the case). The uC is about $6, though I might have to spring for $10 on the prototype as the "best type" is not yet available... >depending on the source impedance you'd probably also want a series >resistor to the MAX232 input. What's the source impedance of a car battery? :-) >BTW: The standard MAX232 will protect fairly well, though there are a >heap of 15Kv ESD rated devices, which also have wider input range and >can handle negative transients quite well. >Hey Bernd, did you get that cheap pump from Dick SMith - rockingham ? No. Not in my budget for this month. All my "spare" cash is tied up in the business at the moment. - -- Real Name: Bernd Felsche Email: nospam.bernie@xxx.au http://www.perth.dialix.com.au/~bernie - Private HP - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ Date: Sun, 26 Mar 2000 02:15:41 -0800 From: Carl Summers Subject: RE: MAP sensing for IR systems Hi Mike, What I have seen happen with IR is extreme pulses in the runner... you will have to use all runners with a line coming from each into a plenum and take your MAP reading from the plenum, you'll probably have to experiment with line size and plenum size to get it to react correctly. hth's - -Carl Summers Click on this link below to see the easiest way to handle internet transactions. https://secure.paypal.com/refer/pal=drsagan%40pacbell.net - -----Original Message----- From: owner-diy_efi@xxx.org]On Behalf Of mike mager Sent: Saturday, March 25, 2000 12:18 PM To: diy_efi@xxx.org Subject: MAP sensing for IR systems What are the practicalities of MAP sensing for an IR (Independent Runner) intake system? 'Theoretically', with symmetrical intake and exhaust, each cylinder has the same MAP, and needs the same fueling and advance, but what happens in the real world? My books fail to address this obscure issue. Thanks, Mike ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ Date: Sun, 26 Mar 2000 18:39:04 From: "Mike (Perth, Western Australia)" Subject: Re: Cheap protection... At 06:25 PM 26/3/2000 +0800, Bernd Felsche wrote: >>Well, another option is to use a protected MAX232 RS-232 input/output >>chip, this already has lots of ESD protection and overvoltage too, > >That's novel. A bit pricey though. Works out about twice the cost >per input as opto. Well that depends - are you doing a one-off or designing a commercial product. In production MAX232's can be got for about A$1.50 depending on volume ? Its relative to the cost of EFI controllers... >I was aiming at $20 in parts for the lot (well, about $25 including >the case). The uC is about $6, though I might have to spring for $10 >on the prototype as the "best type" is not yet available... Sorry, I think I missed an earlier email on this, I take it this is not for an EFI project, what are you building - is this the WI project ? >>depending on the source impedance you'd probably also want a series >>resistor to the MAX232 input. > >What's the source impedance of a car battery? :-) mmmm ! If you are measuring battery voltage then a MAX232 will not work as its a discrete signal conditioner not for measurement of an analog voltage. Since you want to measure battery volts, then a simple divider and large caps would be sufficient... Rgds :) Mike - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ Date: Sun, 26 Mar 100 18:46:41 +0800 (WST) From: Bernd Felsche Subject: Re: Cheap protection... Mike Blakey writes: >Why bother with isolation? DC coupled will be fine. > Use a voltage divider and do the de-bounce/filtering in software. > A simple signal diode from input to Vcc will protect your uP as > the Vcc is low impedance. Cool. Hadn't thought of clamping in that direction. Thanks. The main "problem" I can see with that circuit is that a voltage higher than 5V appears at the uC due to the forward voltage of the 1N4148. It could be worthwhile setting up a "dirty rail" at about 4V (based on the 5V regulated) to absorb the over-voltage currents from all inputs. That would also protect the regulated 5V from strange pulses. - -- Real Name: Bernd Felsche Email: nospam.bernie@xxx.au http://www.perth.dialix.com.au/~bernie - Private HP - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ Date: Sun, 26 Mar 100 18:54:58 +0800 (WST) From: Bernd Felsche Subject: Re: Cheap protection... Peter Gargano writes: >Mike Blakey wrote: >ASCII art? Perhaps you should compose using a fixed font, >say Courier, etc. - this looks just like a lot of scribble >to me, and I'm sure you put a lot of effort into it too!... Well, seeing that he drew it for my benefit... (I only have a "glass tty") and I'm used to squinting when ASCII art goes drunken... >> >> --+--- +5v >> l >> l >> ------- >> / \ >> /___\ 1N4148 >> l >> l >> +---------+ l >> 12v source >-----l 13k l---+------------> input >> input +---------+ l to uP >> l >> l >> +-----+ >> l l >> l 10k l >> l l >> +-----+ >> l >> l >> l >> --+----- GND Is that better? - -- Real Name: Bernd Felsche Email: nospam.bernie@xxx.au http://www.perth.dialix.com.au/~bernie - Private HP - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ Date: Sun, 26 Mar 100 19:35:34 +0800 (WST) From: Bernd Felsche Subject: Re: Cheap protection... Mike writes: >At 06:25 PM 26/3/2000 +0800, Bernd Felsche wrote: >>>Well, another option is to use a protected MAX232 RS-232 input/output >>>chip, this already has lots of ESD protection and overvoltage too, >> >>That's novel. A bit pricey though. Works out about twice the cost >>per input as opto. >Well that depends - are you doing a one-off or designing a commercial >product. In production MAX232's can be got for about A$1.50 depending >on volume ? Its relative to the cost of EFI controllers... I wasn't _planning_ on making a hundred thousand, but if you send me your purchase order, I'll get the wheels turning. :-) Seriously though; in the spirit of sharing knowledge and encouraging education; I'd be happy to offer the proven design to somebody who's be willing to "productionise" a kit. Hands-on experience is a valuable asset, but a student may well have difficulty coming up with more than about $20 for a "gadget" that does little more than help to propel them into geekdom. Seeing that MAX232's retail for about $8 locally and opto-couplers at $1.50, it doesn't make sense to use them for something so trivial. >>I was aiming at $20 in parts for the lot (well, about $25 including >>the case). The uC is about $6, though I might have to spring for $10 >>on the prototype as the "best type" is not yet available... >Sorry, I think I missed an earlier email on this, I take it this is not >for an EFI project, what are you building - is this the WI project ? Nothing that complicated - not brave enough to do something important as my first, blank-slate uC project. It's just a smart courtesy light control with a bag of other functions thrown in to make it complex enough to justify using a uC. :-) The next most ambitious project (if I don't flounder hopelessly on making a light come on) is to "re-do" the cooling fan and aircon-clutch control in my car. It's an absolute rat's nest of heavy wiring back and forth along the front of the engine compartment. That'll look at the analogue voltage from the NTC coolant temperature gauge as well as the stock switches, allowing me to control the fan to operate at *my* setpoints at the speed I choose. (PWM to be added later.) As you can probably see, I like to build my confidence before diving deeply into implementing the EFI - though I will obviously go back and revise the EFI as I learn more about the practicalities of applying uC technology to the real world. I've already figured out that I could have an aircon-clutch output to maximise available engine power while accelerating. >>>depending on the source impedance you'd probably also want a series >>>resistor to the MAX232 input. >> >>What's the source impedance of a car battery? :-) >mmmm ! If you are measuring battery voltage then a MAX232 will not work >as its a discrete signal conditioner not for measurement of an analog >voltage. Since you want to measure battery volts, then a simple >divider and large caps would be sufficient... Well, I'm not measuring analogue voltages. But I will see a total of about 60A fused potential from the battery if I'm not careful. Clipping the input voltage is the trick I've been looking for. A 5-cent signal diode is an attractive option. - -- Real Name: Bernd Felsche Email: nospam.bernie@xxx.au http://www.perth.dialix.com.au/~bernie - Private HP - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ Date: Sun, 26 Mar 2000 11:55:31 +0000 From: Mike Blakey Subject: Re: Cheap protection... >The main "problem" I can see with that circuit is that a voltage >higher than 5V appears at the uC due to the forward voltage of the >1N4148. > Hi bernd, The voltage at your uC will be fine, about .6 < 5v. This is OK for most uP input. >It could be worthwhile setting up a "dirty rail" at about 4V (based >on the 5V regulated) to absorb the over-voltage currents from all >inputs. I've used this circuit on many applications, and for the simple "learning" projects it works great. I've also used the same design on more elaborate projects for taking signals from switch inputs etc. The cost is VERY low and you can easily prove/prototype a design a design without spending a fortune in components and time. Try without the "dirty rail" and if you do get problems, eliminate the noise at source, if possible!. Keep your first circuits simple, and by the time you're ready to tackle a major ECU, you will have enough practical knowledge and confidence. > >That would also protect the regulated 5V from strange pulses. PS. Thanks for re-drawing the circuit, I hope it will be of use to others too. - ---------------------------------------------------------------------------- To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes) in the body of a message (not the subject) to majordomo@xxx.org ------------------------------ End of DIY_EFI Digest V5 #123 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. A non-digest (direct mail) version of this list is also available; to subscribe to that instead, replace "diy_efi-digest" in the command above with "diy_efi".