ELV15 Posted August 17, 2005 Share Posted August 17, 2005 I've got the standard caterham/caerbont tachometer. I'd like to wire in the shift light (the big bright one in the middle of the gauge). There are two dipswitches on the back of the gauge, under the rubber cover. Flipping the first switch makes the light come on. Any idea of how it should be wired/connected? I looked through the archives and found a posting listing the pinouts for the tach, however mine is different and only has 7 wires (the eighth wire seems to be a second ground pin. Grounding it does nothing (as far as I can tell)). I do not have the black/blue shift light wire going into the tach. I do have a shift light wire coming from the ecu, but it does not go to the tach. Any suggestions? Thanks, Tom ELV15 - Tom in California - 200hp duratec powered 2003 Clubsport Build pics here: here Link to comment Share on other sites More sharing options...
ELV15 Posted August 18, 2005 Author Share Posted August 18, 2005 OK, here is some more info I got from Caerbont: This tacho was designed for use with a Rover ecu, some of which had a shift lamp output. The circuit required by Rover was unusual in that the current flowing through the led was quenched by the ecu to turn it off. Current flows from a regulated 12 volt supply, through a 1k5 resistor, through dip switch 1, and through the led to ground. The top end of the dip switch goes to pin 6 of the connector. Hence, if sw 1 is closed, and pin 6 is grounded, current will flow through the resistor to ground through pin 6. When pin 6 is left to 'float', the led turns on. Link to comment Share on other sites More sharing options...
ELV15 Posted August 22, 2005 Author Share Posted August 22, 2005 Ok, So after a bit of experimenting I've got some more info: 1. My tach did not have a wire for the shift light. I had to add one to the connector. The shift light is pin #6. 2. My ECU (MBE 967) switches to ground to trigger the shift light. This is the opposite behavior of the Rover ECU used with the tach. IE: the light is on until the ECU hit's the shift point, then it goes out. Not to usefull!! ☹️ 3. I'm working on a small circuit to invert this behavior. I've got a test scenario up and running. Will post more when it is really working well. ELV15 - Tom in California - 200hp duratec powered 2003 Clubsport Build pics here: here Link to comment Share on other sites More sharing options...
Flymo Posted August 22, 2005 Share Posted August 22, 2005 Could you not use a 12v relay with a set of normally open contacts when energised so when the ecu drops the feed to the relay it goes to the closed postion and puts power to your shift light, iam sure maplins would be able to supply a small relay to do the job Mark BRG 1700 X flow The only caterham in the village Link to comment Share on other sites More sharing options...
ELV15 Posted August 22, 2005 Author Share Posted August 22, 2005 Hi Flymo, Yes, a relay would work. However, besides being overkill, you need to be careful as the relay will have some back flow of current from the coil when it is de-energized and this could damage the circuits in either the ECU or in the tach. Cheers, ELV15 - Tom in California - 200hp duratec powered 2003 Clubsport Build pics here: here Link to comment Share on other sites More sharing options...
Mr Locust Posted August 22, 2005 Share Posted August 22, 2005 A relay and a diode perhaps? Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Chris W Posted August 24, 2005 Share Posted August 24, 2005 Tom I discovered this "inversion" a couple of years ago too whilst fiddling around trying to get the tacho LED to function. I built a transistor inverter which I installed inside the tacho itself and it worked fine. Phase 2 was to connect the tacho LED to a frequency to voltage converter chip which meant I could rotate a knob on the dash and have the tacho LED come on at any rpm value I chose. Phase 3 was to abandon the tacho LED and instead design and build a complete set of gear shift lights which work wonderfully. 10 LEDs (4 green, 3 amber and 3 red) mounted on the top of the scuttle cover the range 4000rpm to 7000rpm in equal steps. (changing circuit values allows a different frequency band to be covered). I also incorporated an LED brightnesss control primarily for night use. The commercial shiftlight sets only usually have only 3 or 4 LEDs and cover a very restricted frequency band (typically, 90% to 100% of max rpm). Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
mav Posted August 24, 2005 Share Posted August 24, 2005 Chris - have you got available a list of parts and instructions for building / installing the shift lights, or better still, can you provide a kit??? Any idea on the cost of your kit vs. aces etc??? Link to comment Share on other sites More sharing options...
Myles Posted August 24, 2005 Share Posted August 24, 2005 and cover a very restricted frequency band (typically, 90% to 100% of max rpm). ...except big-daddy ACES, but then they are at least twice as expensive as the price Chris quoted me a couple of years back for his system... Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Chris W Posted August 24, 2005 Share Posted August 24, 2005 Mav I charge £100 for the finished and completed gearshift lights (you can see them on my website; click below). This also includes connecting them up in your 7 and testing them (at my home location only) nr Dunstable in Bedfordshire. I don't supply a kit. A circuit diagram only would be £30 cheers Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
mav Posted August 25, 2005 Share Posted August 25, 2005 Thanks Chris, but £30 for the diagram is too much for my pocket. Cheers Link to comment Share on other sites More sharing options...
Chris W Posted August 25, 2005 Share Posted August 25, 2005 Sorry Mav but the circuit took a long time to design, prototype build, test, experiment with, redesign and re-test until it worked perfectly. I don't just want to give away all that effort for free. Cheers Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
mav Posted August 25, 2005 Share Posted August 25, 2005 I understand Chris, I'm not criticising. Thanks for the offer. Regards, Martin Link to comment Share on other sites More sharing options...
ELV15 Posted August 26, 2005 Author Share Posted August 26, 2005 Hi Chris, Your other solutions seem quite interesting! Right now I'm just looking for something simple to make the light work. So, your first solution is what I'm working on right now. A simple transistor switch to invert the signal. I've got a breadboard version working but need to make a small version I can actually install. Cheers, ELV15 - Tom in California - 200hp duratec powered 2003 Clubsport Build pics here: here Link to comment Share on other sites More sharing options...
ELV15 Posted September 26, 2006 Author Share Posted September 26, 2006 Wow, so it's been over a year since I posted this question. I've finally gotten around to this project and have a working circuit. My shift light now works! Here is a a schematic of what I did: here Enjoy! err, the LED appears in the schematic upside down, but I'm sure you get the general understanding of how it should work. ELV15 - Tom in California - 200hp duratec powered 2003 Clubsport Build pics here: here Link to comment Share on other sites More sharing options...
Chris W Posted September 27, 2006 Share Posted September 27, 2006 Tom There must be an error on the resistor values on your drawing as it shouldn't work as drawn (ignoring the reversed LED). When the ECU switches to ground, the resistor chain R3/R4 will create a voltage of only about 0.5 volts at the base of the transistor. This is not enough to switch the transistor ON. Even if in practice the supply voltage is closer to 14v rather than 12v (due to the alternator)the base voltage will be only marginally higher. The voltage at the emitter of the transistor will therefore be at virtually earth potential so no current will flow through R2 and the LED will not illuminate. I suspect that R3 is 1.2K (rather than 12K) which would create an emitter voltage of about 2.8v which would give an emitter current of about 3mA. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
ELV15 Posted September 27, 2006 Author Share Posted September 27, 2006 Hi Chris, Thanks for your notes. It does work...although I really don't know what I'm doing! 😳 The weird bit is that the tach shift light is setup to turn the light off when it grounds. ie: the reverse of what the ECU is doing. So I designed this circuit to have the transistor always on - until the ECU triggers the shift light pin, at which point the ECU pulls the base low - effectivly switching the transisor off - and the light comes on. Please let me know if this is really not the way to do this! 😬 Oh, and I'm sure I left out parts of the circuit...the LED certainly has a ground somewhere inside the tach... ELV15 - Tom in California - 200hp duratec powered 2003 Clubsport Build pics here: here Edited by - ELV15 on 27 Sep 2006 02:31:25 Link to comment Share on other sites More sharing options...
Chris W Posted September 27, 2006 Share Posted September 27, 2006 Hi Tom The way it's drawn is not the way you describe its working. When the ECU grounds, the transistor will switch OFF and therefore the LED will extinguish. If it is working the other way round, you must have a PNP transistor rather than the NPN drawn. ie: an NTE 383 rather than an NTE 382. As it's drawn, the LED will be ON all the time that the ECU switch is OPEN, ie: BELOW the trigger point revs. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
ELV15 Posted September 27, 2006 Author Share Posted September 27, 2006 Hi Chris, Thanks again for the input! I've revised the schematic and hopefully it will now make more sense. Here is the new improved version: here (edited to fix url) ELV15 - Tom in California - 200hp duratec powered 2003 Clubsport Build pics here: here Edited by - ELV15 on 27 Sep 2006 16:20:05 Link to comment Share on other sites More sharing options...
Chris W Posted September 27, 2006 Share Posted September 27, 2006 Ah... that's make sense now Tom. cheers Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
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