Honda Shadow Forums banner
1 - 13 of 13 Posts

· Registered
Joined
·
11 Posts
Discussion Starter · #1 · (Edited)
Hi I'm trying to make a tach for 94 vt1100c following someone else's schematic. Someone did it for a v8 chevy then a guy copied it for his motorcycle. Do you guys know what an ignition coil negative wire is on my bike? Bl/w, bl/y, y/bl?
 

Attachments

· Registered
1983 Honda vt750 Shadow
Joined
·
20,290 Posts
Each coil has a black/white wire and those are the battery power.
The other wire on each coil is the negative, or the signal from the ICM to fire the coil.
Pick one of those others, blues or yellows.
 

· Registered
Joined
·
765 Posts
From my reading of the manual, the ICM puts out some pretty potent pulses to the ignition coil primaries. The manual was talking about using a peak reading setup with a 200 VDC capacity to test ICM output. This isn't an old fashioned 12V points closing and opening ignition, it's high energy. Either the tacho. will need to be able to handle the pulse amplitude, or you'll want a buffer circuit to reduce the pulse to manageable level.

I'm surprised that there isn't a tachometer accessory output from the ICM.

Didn't the 80s Shadows have tachometers? I wonder how those were setup?
 

· Registered
Joined
·
11 Posts
Discussion Starter · #4 · (Edited)
From my reading of the manual, the ICM puts out some pretty potent pulses to the ignition coil primaries. The manual was talking about using a peak reading setup with a 200 VDC capacity to test ICM output. This isn't an old fashioned 12V points closing and opening ignition, it's high energy. Either the tacho. will need to be able to handle the pulse amplitude, or you'll want a buffer circuit to reduce the pulse to manageable level.

I'm surprised that there isn't a tachometer accessory output from the ICM.

Didn't the 80s Shadows have tachometers? I wonder how those were setup?
I was wondering if this bike was CDI or not or what voltages were involved. I initially thought it was something like 1000VDC then saw 12VDC wires in the diagram for the bike. Then there is an optocoupler used that I thought was used to isolate the ignition circuit from the controller. That optocoupler diagram had me confused with motorcycle ground connected to the cathode then a "Negative" coil wire connected to the anode...

The forward voltage through that optocoupler diode is just 1 volt

The person who made this originally ditched the optocoupler because the truck had a tach output on the ECM and it was direct connection to the controller. now ill be looking for a pinout

Rectangle Orange Font Magenta Logo


maybe its just the resistor saves the day
 

· Registered
Joined
·
3,273 Posts
Actually the ICM applies a ground on the yellow-blue and blue-yellow to fire their respective coils. The yellow-blue may have the fuel cut relay involved also if it has one, to use the same intermittent ground signal to keep the relay energized long as the motor is turning. they're the negative side of the coil primary winding.
 

· Registered
1983 Honda vt750 Shadow
Joined
·
20,290 Posts
Yes the older bikes like my 1983 are an improved points and condenser setup using a transistor instead of points.
And they do ground the negative to fire.
The newer ones are true CDI with a high voltage capacitor output to the coil. I never have had one to experiment.
But many guys here have put a tach on their bikes and I never heard of an electrical blow up.
Not sure how it is protected.
 

Attachments

· Registered
Joined
·
765 Posts
But many guys here have put a tach on their bikes and I never heard of an electrical blow up.
Not sure how it is protected.
Maybe the tacho inputs are just well protected? Seems like even old school 12V points systems were dealing with a lot higher transient voltage pulses than 12V because of the inductive spike.

I recall looking at the primary signal when I was trying to figure out the fuel pump "relay" on my 1100. The pulse amplitude was high (negative), but the spike was very short, it wasn't a whole lot of energy.

Then there is an optocoupler used that I thought was used to isolate the ignition circuit from the controller. That optocoupler diagram had me confused with motorcycle ground connected to the cathode then a "Negative" coil wire connected to the anode...

The forward voltage through that optocoupler diode is just 1 volt

The person who made this originally ditched the optocoupler because the truck had a tach output on the ECM and it was direct connection to the controller. now ill be looking for a pinout

View attachment 305678

maybe its just the resistor saves the day
My understanding of optocoupler is that it decouples the circuit from the input by interposing an LED driving a phototransistor. Like this:
Rectangle Product Slope Font Parallel

The input signal lights the LED, and the max amplitude that the phototransistor will deliver is dependent on the right side power supply voltage, not the input signal.

What you drew was equivalent to just the left side, input side of this sample circuit. The LED is a diode, so would have a fixed voltage drop, 0.70V commonly. In series with the 10K resistor, all the voltage except that 0.70 V would appear across the resistor.

I understand enough about electronics to make stuff work, but I also occasionally let the smoke out, so please be careful with my advice, as you hopefully would with any free advice found on the internet.

Having said that, here's another idea. I think that the fuel pump supply wire from the fuel pump "relay" that oldguy mentioned, is essentially what one might want to drive a tacho. That gadget sends a fat 12v pulse to the fuel pump every time the (front?) cylinder fires. It takes care of buffering the high amplitude negative spikes that the coils like, and you wouldn't be parasiting any power from the ignition circuit.
 

· Registered
Joined
·
3,273 Posts
That is an electronic "relay", The black wire is 12v power from key, Black-blue is power to the pump, yellow-blue is relay control negative tied to the yellow-blue from coil negative to ICU. I don't see why the tach wouldn't work hooked to the yellow blue if it's looking for a momentary ground to work. These relays, being electronic, may have all kinds of circuitry to keep the pump going as the control is going to see the ground as something like a low ac voltage with a variable frequency. Pretty sure you won't get a good signal from the pump power. Why doea everyone obsess over a tach anyway? just one more thing to take your eyes off the road...
 

· Registered
Joined
·
11 Posts
Discussion Starter · #10 ·
If that wire from the relay to the pump has 12v every time the spark fires I'm going to try that wire with a resistor into that high-speed optocoupler.

Have a display ready
View attachment 305721
If that wire from the relay to the pump has 12v every time the spark fires I'm going to try that wire with a resistor into that high-speed optocoupler.

Have a display ready
View attachment 305721
That is an electronic "relay", The black wire is 12v power from key, Black-blue is power to the pump, yellow-blue is relay control negative tied to the yellow-blue from coil negative to ICU. I don't see why the tach wouldn't work hooked to the yellow blue if it's looking for a momentary ground to work. These relays, being electronic, may have all kinds of circuitry to keep the pump going as the control is going to see the ground as something like a low ac voltage with a variable frequency. Pretty sure you won't get a good signal from the pump power. Why doea everyone obsess over a tach anyway? just one more thing to take your eyes off the road...
The black/blue wire here. 16 hz for 1000 rpm. 7.75 volts at center of that slope I think. I'll tailor the opto to 7.5 to 9 volts input and see if the controller counts
 

Attachments

· Registered
Joined
·
765 Posts
The black/blue wire here. 16 hz for 1000 rpm. 7.75 volts at center of that slope I think. I'll tailor the opto to 7.5 to 9 volts input and see if the controller counts
It's interesting how the fuel pump signal goes negative. Maybe that is the inductive effect from the fuel pump solenoid when the power is cut off? I think these are solenoid type linear pumps, and not rotating type. Mine definitely sounds like a "jiggle pump".

Schematic Rectangle Font Engineering Parallel



Some time ago, Swifty posted a simplified diagram of what is inside the fuel pump "relay", and it looked to be basically a thyristor triggered by a transistor. https://www.hondashadow.net/attachments/fuel-cut-relay-png.295904/ But I don't see that simplified diagram as expaining why the fuel pump signal is in the form of a saw tooth wave? It seems to get that result there must be a capacitor storing the energy that gets dumped through the thyristor?

It might be interesting to look at the pump relay output signal vs. the input signal from the ignition. I intended to do that, when I was scoping out the fuel pump "relay" on my machine, but never got back to it. It looked to me like the ignition pulse was less than .002 sec long, but I never went back to look at the fuel pump relay output with an appropriate time base setting. Fuel pump advice , to could use a lil help

I'm embarrassed to admit that reading my own post is hurting my brain to understand now. You really have to speak that language at least somewhat often or you lose it. My brother is an EE who like to play with Rasberry Pi's for fun, but the Arduiino makes a lot more sense for what you are trying to do.

Is this a college course project?
 

· Registered
Joined
·
11 Posts
Discussion Starter · #12 · (Edited)
That pic is misleading. Here's a different one. It doesn't go negative it looks like the spike is just ~14.6v battery voltage then drops to 1-2 volts at the end. 5v/d. The 7.82 vdc I think is the mean of all the voltages on the wave. Under left glare is a rectangle displayed that shows zero reference.

I would not expect a square signal. There are circuits I've seen which turn it into more of a square. The scope is in parallel with the pump too that might affect the wave in some way.

I have a total count working with a pushbutton inside but on the bike when I hold the black and blue wire to the anode of the opto the controller counts once and stays on. I'll get rid of a 50 ms delay in the program tomorrow. That can't be in there to work. Maybe move input from a check of the input every scan to a interrupt so it doesnt have to occur when it is bring checked.

Not a college project or anything.

Vertebrate Automotive lighting Font Vehicle door Gas
 

· Registered
1983 Honda vt750 Shadow
Joined
·
20,290 Posts
The 2004 Honda Common manual has that information about the relay and pump.
 

Attachments

1 - 13 of 13 Posts
Top