fitting rev counter to car that does not have one - Page 1
Forum section: electronics / general

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 12:51:37 pm
content: I just bought a ford fiesta MK4 (2000) that does not have a rev counter, Any way I can fit a rev counter ? It does not have to be in the dash, I don't mind an external panel etc, any kits out there ?

author: G7PSK
author_rank: Super Contributor
timestamp: February 22, 2012, 01:19:58 pm
content: There is no sender for a rev counter in these cars you need to find a pulse and use an external rev counter.

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 01:23:48 pm
content: yes i need to either put something reflective on the alternator belt and use a opto system or hopefully pick up pulses from the spark plug cables, if i have a coil on one cable that is one pulse every two revolutions.

author: david77
author_rank: Frequent Contributor
timestamp: February 22, 2012, 01:31:51 pm
content: Back in the 80's all the electronics magazines used to publish dozens of rev counter circuits. Most of them used a coil wound around the HT lead from the ignition coil to the distributor cap. Then all you need to do is bring that pulse up to TTL level and count it. From that you can calculate the engines revs, I'm sure I've got the details in an old Elektor mag at home. I remember they used 50Hz mains frequency to calibrate the rev counter. If it helps I could look it up.EDIT: I managed to fit a rev counter into one of the dummy buttons of a MK2 Golf once, sadly the circuit's gone to the knackers yard together with the car.

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 01:36:39 pm
content: Quote from: david77 on February 22, 2012, 01:31:51 pmyes please, that is just what i'm after, I've seen kits around the net but they are like £50+ which is silly. Are there IC's that do counting and displaying ? or would i be stuck with coding an MCU if I made my own from scratch ?

author: Balaur
author_rank: Unknown
timestamp: February 22, 2012, 01:40:15 pm
content: Disclaimer: I'm not familiar with your car, so no idea if the following comments apply.It looks like the on-board diagnostic connector on your car is OBD2-compliant. Maybe the live data exported by the port also contains revs information. (My Rover 400 does and i'ts not even OBD2)In that case, you can put something together from a OBD2 reader or find a pre-made OBD2 dashboard.Otherwise, the alternator AC outputs could be exploited to provide an indication of the engine speed. Obviously, you will need to compute a proportionality factor.The final suggestion, if you want to go for the easy way, is to buy a pre-made tachometer. These devices connect on the spark plug cables, as you suggested yourself:Example

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 01:44:56 pm
content: well i think it woyuld be easier to sense off a sparplug cable than use the diagnostics connectors, that unit you linked too is better as it does more and $65 is not like £50 but I'll have to look at postage etc from US

author: david77
author_rank: Frequent Contributor
timestamp: February 22, 2012, 01:49:25 pm
content: The one I built used 40xx or TTL IC's. It should be rather easy to fit all that into a single MCU, though.I can't remember the details off the top of my head, though.In theory you could just count the pulses from the HT and use the idling revs to calibrate the counter. Maybe not the most accurate way to do it but close enough, I'd say. The engines probably idles somewhere between 600-900 rpm.Another way might be to find out if the car was available with built in rev counter. Often they just use another instument binnacle but leave the rest of the electronics in place, so a retrofit with a instrument with rev counter may be possible.I don't know if Ford do this, however VW do. That is the most elegant but probably also the most expensive way to get a rev counter.

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 01:53:22 pm
content: Quote from: david77 on February 22, 2012, 01:49:25 pmHey, I'm a quality inspector - don't go suggesting i calibrate against something that can vary up to +50%Well my panel looks nicely filled out its not like there is room for a rev counter. I also don't want to mess with it at that level and loose my mileage counter as it could mean that later to car is considered to be tampered with.

author: Teknotronix
author_rank: Regular Contributor
timestamp: February 22, 2012, 02:37:34 pm
content: Here are some pre made cables and breakout boxes:http://www.obd2cables.com/products/obd-cables/obd-ii-cables/Here is a homebrew option as well:http://www.nerdkits.com/videos/obdii/

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 22, 2012, 02:48:40 pm
content: I run a ScanGauge II in my vehicle. It connects with ODB II port and gives me all kinds of data. I generally run Instant and AVG MPG, Gallon/Hr, and RPM. You can set to display any 4 data values at a time. There are also vehicle dependent fields you can activate, such as Ox sensor values, etc.

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 02:54:59 pm
content: Quote from: sacherjj on February 22, 2012, 02:48:40 pmi like it, just need to find a dealer and price - is it expensive ?

author: G7PSK
author_rank: Super Contributor
timestamp: February 22, 2012, 03:02:43 pm
content: How's this on ebay £17-00http://www.ebay.co.uk/itm/Rev-Counter-52-mm-diameter-Tachometer-Kit-Car-LED-/180729783632?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2a1455a550#ht_144

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 03:08:07 pm
content: Quote from: G7PSK on February 22, 2012, 03:02:43 pmnow thats cheap, might get one, or save for a scanguage

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 22, 2012, 04:14:00 pm
content: Quote from: Simon on February 22, 2012, 02:54:59 pmScan Gauge II is ~$160 US. Others are ~$80-$100. I'm slowly getting that back by the changes it made to my driving style to be more efficient.Also works as a code reader for OBD fault codes.

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 04:16:33 pm
content: how much will it tell me about a fiesta though ? i have a digital mileage counter but will i get the MPG info etc ? i wanted engine/coolant temp too so might be worth it

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 22, 2012, 05:44:20 pm
content: Quote from: Simon on February 22, 2012, 04:16:33 pmFrom what I'm seeing, most people are recommending the Scan Gauge II over the newer and simpler (slightly cheaper) one. Here is the page to research the capabilities.http://www.scangauge.com/products/scangaugeii/

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 05:59:12 pm
content: I found this:http://www.amazon.co.uk/SainSpeed-TurboGauge-Automotive-Computer-Backlight/dp/B005WRXITG/ref=sr_1_99?ie=UTF8&qid=1329932622&sr=8-99What I'm saying about MPG, either the car provides this data or it has to provide information on the amount of fuel used (and if that comes via the main fuel gauge good fricking luck) and the distance traveled and work it out. I am one of those people that works out my MPG at each complete tank refill

author: Chet T16
author_rank: Frequent Contributor
timestamp: February 22, 2012, 06:22:59 pm
content: Most cars will use fuel injector period and duty cycle in calculating consumption.I've seen rev counters that plug into the cigarette lighter and are able to sense the frequency from the alternator. Personally I'd be going to the coil trigger wire, i think the 2000 fiesta has coil packs which might mean no ht lead.

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 06:25:31 pm
content: oh right, surely any spark plug lead can be used too, so long as the unit knows where the signal comes from, main HT lead = 2 pulses per rev, spark plug HT lead = 1 pulse every 2 revs

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 06:28:30 pm
content: There is also:http://www.ebay.co.uk/itm/Car-OBD-II-Diagnostics-Tool-Multi-Function-Information-Display-/180770581801?pt=UK_Diagnostic_Tools_Equipment&hash=item2a16c42d29#ht_6920wt_1112

author: Zero999
author_rank: Super Contributor
timestamp: February 22, 2012, 06:43:02 pm
content: I wonder how much AC ripple there is on the 12V system?You may be able to amplify the ripple on the car's DC rail and count it. Any microcontroller with a crystal clock should give accurate enough results.Perhaps you should connect your 'scope to the car.

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 06:47:29 pm
content: would prove interesting, although I like the OBD display idea as I want to see engine temp as well and if other stuff is available thats good

author: Chet T16
author_rank: Frequent Contributor
timestamp: February 22, 2012, 06:53:05 pm
content: OBDuino it is so! Only reason I haven't tried it is because of all the cars here the only one modern enough to have OBDII is firmly in the no tinkering zone, bosses orders

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 06:55:21 pm
content: well i hope I have an obvious plug and don't need to tear the car apart to find it

author: Zad
author_rank: Super Contributor
timestamp: February 22, 2012, 07:16:41 pm
content: I think on that model Fiesta, the diagnostic connector is behind the kick panel in the passenger foot well. Don't forget that for every HT system, there is an LT side which is easier/safer to sense.

author: Simon
author_rank: Unknown
timestamp: February 22, 2012, 07:17:48 pm
content: Quote from: Zad on February 22, 2012, 07:16:41 pmyou mean up the front where they normally bury the ECU ?

author: Unknown
author_rank: Unknown
timestamp: February 22, 2012, 09:17:59 pm
content: Quote from: Simon on February 22, 2012, 06:47:29 pmFYIhttps://www.eevblog.com/forum/general-chat/odb-ii-vehicle-diagnostics-circuits/

author: Zero999
author_rank: Super Contributor
timestamp: February 22, 2012, 09:22:47 pm
content: I wonder if you could do it acoustically? Maybe a small microphone could be used to listen to the engine.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 23, 2012, 06:07:39 am
content: Quote from: Simon on February 22, 2012, 01:53:22 pmGee,you must have horrible unstable mains--about 4% short term would be pretty much the case in West Oz!Average is better!

author: Psi
author_rank: Super Contributor
timestamp: February 23, 2012, 06:29:22 am
content: i've not read the whole thread, but you should be able to lookup the ECU pinout and find the pins that drive the coil packs.That way you wont need to screw around with HT voltages. It will either be +5 logic or +12v fet/transistor driven outputs.You might also be able to count the pulses on one of the injectors to work out RPM.

author: Simon
author_rank: Unknown
timestamp: February 23, 2012, 06:46:05 am
content: Quote from: vk6zgo on February 23, 2012, 06:07:39 amsorry I did not quote enough, I was referring to using the idle speed as a calibration reference

author: damo
author_rank: Contributor
timestamp: February 23, 2012, 07:04:16 am
content: I always loved the LED tacho's using the 2917 and twin 3914 as outputs

author: david77
author_rank: Frequent Contributor
timestamp: February 23, 2012, 07:28:30 am
content: I've had a look through my Elektor collection from the 70's and 80's and found a couple of rev counters.From simple one with just a analogue meter as readout to one with dozens of LED's driven by several LM391x.All these circuits actually take their counting impulse from the LT side of the coil, I remembered that incorretly. Makes more sense anyway.I've always secretly lusted for this in my Golf:http://imageshack.us/photo/my-images/20/digifitzengolf2gti.jpg/Very K.I.T.T.

author: Rerouter
author_rank: Super Contributor
timestamp: February 23, 2012, 10:06:23 am
content: also being an older vehicle, 2000, you could look to see if it has an on board diagnostics plug, eitheres an OBD2 style, or a round one, before OBD2 became a standard, some vehicles ran there rev output to the plug,

author: BravoV
author_rank: Super Contributor
timestamp: February 23, 2012, 11:01:57 am
content: I remember I did make a circuit quite long time ago maybe in 80s where car still using carburator and no smart electronic, using the National ic LM2907.Its very simple and just adding few discrete components, it will ouput a voltage that will work with a retro style analog voltmeter or LM3914 for digital display and its dirt cheap too.

author: Unknown
author_rank: Unknown
timestamp: February 23, 2012, 11:05:50 am
content: Quote from: vk6zgo on February 23, 2012, 06:07:39 amThe variation may well be a reference to the Ford Fiesta!

author: Simon
author_rank: Unknown
timestamp: February 23, 2012, 11:08:10 am
content: the variation was in reference to the 600-900 idle rpm I should "calibrate" too, that is not a stable reference

author: GeoffS
author_rank: Unknown
timestamp: February 23, 2012, 02:28:39 pm
content: I've got a Scangauge II installed in my vehicle (Mercedes Sprinter) and it's well worth the $165 I paid for it. Apart from all the obvious things to display - like RPM, it has an inbuilt fuel economy/cost calculation that's pretty accurate.When (if) I get organised, I'm planning to build an OBD II interface using the ELM327 chip. The programming to use this is very straight forward and could easily be used to build an RPM counter (is that different to a tacho?)A quick browse indicates that your vehicle should have an OBD port, not sure if it's OBD II or I though.

author: Simon
author_rank: Unknown
timestamp: February 23, 2012, 02:39:08 pm
content: well i've ordered this:http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=260867654675&ssPageName=ADME:L:OC:GB:1123and am copiously crossing fingers

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 23, 2012, 04:14:53 pm
content: Quote from: GeoffS on February 23, 2012, 02:28:39 pmIn the US, all vehicles 1996 or newer were required to have ODB II. I'm not sure what the requirements outside of the US were, but I expect a 2000 model anywhere to have one.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 24, 2012, 01:09:21 am
content: Quote from: Simon on February 23, 2012, 06:46:05 amSorry,my mistake,I didn't read carefully enough!Another way to calibrate would be to run the engine at a steady speed,hang an analog Oscilloscope across the pulse output from the ECU,(or just pick upradiatedspark plug pulses).If the 'scope has a "vert o/p" connector you could then read the frequency with a frequency counter.Come to think of it,with a DSO, you could read it directly---even an "el cheapo" should be close enough for RPM!

author: Simon
author_rank: Unknown
timestamp: February 24, 2012, 07:03:08 am
content: true my rigol can pickup a spark signal and count it. I've bought a comercial unit now that I've learnt just how much more info I can get off the OBD bus

author: SgtRock
author_rank: Unknown
timestamp: February 24, 2012, 07:15:40 am
content: Dear Simon:--Here is a very simple, easy to calibrate, cheap kit.http://www.apogeekits.com/digital_tachometer_kit.htm--And an even better one, better reading and IR driven. Also a cheap kit.http://ikalogic.com/ika_tach.php"He didn't know where he was going. But he knew where he was wasn't it."Lord Buckley 1906 1960Best RegardsClear Ether