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J.D., In a article submitted by Lee Swanger it mentioned that you had some input on the design of of the tach driven by the vehicle ESS.
I installed identical products as in the article to no avail the tach will bob a little when one turns on the switch recognizing the 12V but thats where it ends it is non responsive to rpm. I e-mailed Lee and he recomended since they are so cheap to replace the transistor.
My question is where can one find info on how they work? I am assuming that it works in this case as a switch. it has Base, Collector and Emitter.I am curious as to the function of each.
Bought a oscilloscope on e-bay today so I can obtain the values from the ESS and compare to his.
Its probably something simple that I'm overlooking at least I hope so. :confused: Thanks in advance.........Merle
mahagie@iowatelecom.net
The Dr.Lee ckt is to drive a tach which requires a pulse input from a transistor ignition system, based on four pulses per crank revolution.
The oem GM tach in Blazers, Subs, pickups, and etc. will function with this ckt. Some vehicles were six cylinder equipped, which tach would require modification from three to four pulses.
The 2.2uf cap decouples the ESS inductor from the base biasing ckt, passing only the ac component. This switches the collector, pulled up to 12vdc by the 1k ohm resistor, to ground (emitter) at the ESS rate.
The 1k ohm resistor provides suitable drive for most tachometers.
Your ESS should put out about 1/2volt peak-to-peak ac pulse at 300 idle rpm, to over 5v p-p at 1700 rpm. These equate to idle @ 600 engine rpm, and full out @ 3400rpm.
The ESS inductor is isolated from engine ground, so both leads will require connection to the tach buffer - signal and dc common (ground).
The tach drive buffer requres dc positive (+12v), dc common (ground) and tach drive signal connections.
Tach drive output should be a squared pulse from 0v to +12v, ground based.
The transistor collector is center lead and mounting tab, which must be isolated from chassis ground.
As-connected circuit values =
Base voltage is about +1 volt
Collector voltage is +12v, depending on tach ckt
Emitter is 0 volts, ground
ESS signal lead at capacitor is 0 volts.
For reference, what brand is your tach, and do you know the specs?
jd
jd, I have everything the same as Dr. Lee same tach same ess/vacuum pump, article followed to the letter with the exception that mine don't work :(
The only dif is my tach is VDO 333-153B Dr Lee didn't mention the B in his article,doubt if it makes a dif.
Look in feature articles Dr. Lee's article appears there and thats the diagram I followed.
jd,in reading your reply a little more in depth I notice you say the ess ground has to go to the tach buffer.
this could be the problem here as I interpreted his diagram that all the grounds ess,15k resister,transister emmiter and tach went to chassis ground.
I took the ess common as a ground and grounded it to the engine.
Now the confusing part, using the diagram it shows 4 leads to what I thought was chassis ground how many are actually ground and which are actually common?
An electronics person I'm not but would like to understand more, I'm more into electrical 110/220/208/460Vthose I understand more....Merle
Electronic circuitry has two common reference points - DC common which is power supply and signal return, and chassis ground, or earth ground for AC power considerations. In some uses they can be connected together, some not.
I teach electrical separation in equipment seminars.
But, I have to forcibly remember dc common\battery negative is called frame\battery ground when typing automotive stuff.
My apologies for the confusion.
Circuit schematics, as drawn, seldom represent actual wiring practice.
All grounded points as drawn are chassis\engine ground, which is dc common, but not necessarily grounded at four separate locations.
In construction, my preference would have brought the two leads (inexpensive 18awg zip cord pair is suitable) from the ESS into the cab, tied them to signal and common\ground at the module, then connected module power and chassis ground, and tach power, signal and ground at the module. It's good electronic wiring practice for reliability and ease of troubleshooting.
One power, one tach signal in, one tach drive out, and one ground.
Also makes it easier for me to remember, day after tomorrow. ;)
However, the ckt will function normally with one ESS pin grounded to the engine and the module grounded to the instrument panel or body.
You might call VDO about that "B" on the tach - it could designate different signal level\type requirements.
Tell them you have a positive +12v signal, ground based, 300hz to 1700hz max.
I'll explain the transistor this evening.
jd
Later......
Sorry 'bout that - the salt had started pouring out of the chute, and I had to get back to the mine.
The NPN transistor in this ckt is a switch - ESS puts a positive on the Base turns the device on; Collector is in effect shorted to the Emitter, and the tach sees low voltage.
On-current thru the 1k ohm resistor is I=E/R
12v/1000ohms = 12ma
ESS drops the positive on the Base turns the switch off, Collector swings back to +12v, the tach sees hi voltage.
12 volt transitions low - hi - low at the ESS rate is suitable input a tach meant for ignition service.
jd
[ 10-21-2003, 05:31 PM: Message edited by: gmctd ]
jd, Thank you very much for the info,It would appear that circut wise I have installed everything in the correct manner.
But seeing as how it doesnt work I must search for reason why.
By any chance are resisters polarity sensitive?
(Dumb question borne from desperation)
If one were at this time to try and point finger at most likely suspect what would it be?
Sorry for the ignorance induced dumb questions.
BTY I even copied the article down to the breadboard,is it suitable for final use or just for experimentation?
The more I study the diagram by Dr. Lee the more confusing It becomes,because as I understand it the base terminal recieves the signal from the ess, the emmiter through the path to ground makes up the switch sending the pattern from the ess on to the tach input through the collecter terminal,the confusing part is as signal travels from the C terminal it picks up a connection from the 1K resister dosen't this contaminate the signal? Does it not confuse the signal path theres no diode here to assure path, I would think that the path from the C terminal on transister should be uninterupted to the tach input, that its output voltage should be predetermined by its input voltage (here again affirming my ignorance)
Thanks again for your help.......Merle
[ 10-22-2003, 10:41 AM: Message edited by: mhagie ]
No sweat on the questions, Merle - ask away! smile.gif
The breadboard is suitable for testing - I would solder up a 'module' assembly after everything checks out.
I can describe solder connections for a small sturdy module if you like, not much larger than the transistor itself.
The resistors are non-polar, but a polarized capacitor should be wired positive (+)lead to Base connection.
The TO220 transistor lead configuration, with plastic side facing you and three leads down or toward you, is -
1 = Base 2 = Collector 3 = Emitter
Usually, a tachometer wants to see a ground-based signal going positive. In this ckt, we 'pull' the tach input positive thru the 1k resistor connected to the Collector. When the ESS signal drives the Base more positive than the 220k\15k bias, the transisor 'switch' turns on, 'shorting' the Collector to the Emitter. This pulls the positive voltage on the 1k resistor\Collector junction to ground. The ESS then drives the Base negative with respect to the bias, turning off our switch, and the Collector is again pulled positive by the 1k resistor.
Voila!! A ground-based signal going negative -positive, negative - positive, 4 times per crank revolution. Just what the Good Tach Doctors prescribed.
Also our very own Good Doctor, the Clevite Kid! ;)
So.....troubleshooting -
Circuit connected and powered up, engine off, negative voltmeter lead to ground, tach signal lead disconnected from Collector -
Base = approx +0.8 volts bias
Collector\1k junction = +12.6 or battery volts
Emitter = 0 volts or ground
ESS\capacitor junction = 0 volts
Connect tach signal lead to Collector, previously-measured voltage should not drop appreciably - one volt = 1 milliamp would be greater than 10k tach input impedance, which is good.
Scope vertical input set for 1 volt per cm, DC coupled, sweep set for 1ms or so, trace set 1 square below center grat, 1meg probe
10meg probe? Set vertical amplitude to .1v\cm for indicated levels.
Crank engine, scope will display about 1volt peak to peak signal at ESS\capacitor junction.
Same at capacitor\Base junction, but shifted upward about 1 volt
Signal at Collector\tach junction should be same frequency as input but with 12volt amplitude, low-level peak to hi-level peak.
Ok - works fine, lasts a long time!
Still wont drive the tach? All tachs are not equal - some require inductive input, some indicate 1/3rd ac phase frequency in the alternator, some require higher voltage signal from igniton system, some require photocell loading, etc.
VDO can answer suitability questions concerning that 'B' suffix tach.
From there, it's happy motoring.
jd
jd,Many thanks for such prompt replys, in the next few days I should be able to scope out (pun) the problem, in the meantime thanks again.
Also I called VDO this pm and they told me they never changed the tach values so mine be the same as the good Dr. Lee.
I also have the identical engine to his w/the exception mine is in a 80 4X4 w/a new Banks 6.2 turbo.
Later ...........Merle :D
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