speed pulser inside the speedometer head, explanation post

[lostforawhile]

I wrote this in response to a question Dr. Snooze had about one of my posts, these cars having a cable driven speedometer, of course have no VSS, but they do have a speed pulser inside of the speedometer head, that is driven directly off of the cable.


This is an old Junk cluster I took apart to show the parts inside, I'm not sure if it's an LX or LXI, but it does have the diode installed for the cruise control, so it's not a DX. It also is an NS cluster.


this is the connection for the speed pulser on the back of the cluster, the left screw is ground, and the orange wire is it's output.




inside the box connected to it, we have this complex looking circuit,




which when flipped over.................







wait for it.........








contains nothing but a single diode








the diode for the cruise control, is on the actual cluster trace, here, DX cars have this same trace, but the diode is simply missing.








inside the speedometer head, these are the connections for the speed pulser







this is the actual pulser itself, it's simply a reed switch, that is triggered by a flying magnet, every single time the speedometer cable makes a rotation.





where the magnet is imbedded






this is the same box off of a dx, both have the same speed pulser, but the DX box contains, guess what,a diode!!





if you ever wanted to change your speedometer to an electronic one, most will accept ground triggered inputs, most aftermarket, so all you would have to do is mount an old speedometer, somewhere behind the dash, and tap those two terminals for your signal.

[lostforawhile]

bump for Dr. Snooze, here is your pulse generator you asked about ok, this looks to be from an LX, as the LXI wiring diagram shows a power wire going into the speed sensor amplifier, but it also shows three generic marked grey wires from the speed pulser, which dont actually exist, did the JDM versions of these cars come with an actual VSS instead of a cable? I wonder if the LXI speed sensor amplifier has an actual 5 volt square wave output? someone needs to hook one to a scope if it does, that could be useful to a lot of people

[Dr_Snooz]

Forgive me. I don't remember the question I asked.

[lostforawhile]

I think you asked what the speed pulser was or something

[Oldblueaccord]

Well just for S and G.


https://www.3geez.com/forum/project-c...e-cluster.html

da answer.

AutoSpeed - Performance Electronics, Part 5

[lostforawhile]

Well just for S and G.


https://www.3geez.com/forum/project-c...e-cluster.html

da answer.

AutoSpeed - Performance Electronics, Part 5

thats what I was trying to figure out, but I believe the LXI has the electronics that are missing in these, and converts the signal directly to a 5 volt square wave, like a modern VSS, on the lx and dx it's simply an emissions signal when the car reaches 5 mph I believe, the carb computer counts the pulses to calculate 5 mph. I'm trying to verify that the LXI does have a 5 volt square wave directly out of the box. That could be really useful for a lot of things. I have a spare reed switch put up, they are mechanical and eventually parts of the switch will break off

[Oldblueaccord]

You have a meter and the electrical smarts. follow the blurb it gave some good insight on what it does and how to test for it.

[lostforawhile]

You have a meter and the electrical smarts. follow the blurb it gave some good insight on what it does and how to test for it.

I dont have an LXI module, only a dx and an LX one, all they have inside is the diode. the circuit board is there, but no components, I was wondering if all that circuitry is there on the LXI and is basically a VSS out

[gp02a0083]

thats what I was trying to figure out, but I believe the LXI has the electronics that are missing in these, and converts the signal directly to a 5 volt square wave, like a modern VSS, on the lx and dx it's simply an emissions signal when the car reaches 5 mph I believe, the carb computer counts the pulses to calculate 5 mph. I'm trying to verify that the LXI does have a 5 volt square wave directly out of the box. That could be really useful for a lot of things. I have a spare reed switch put up, they are mechanical and eventually parts of the switch will break off

silk screen marks can be used as indicators, there are a few resistors, capacitors, zener diodes and a triode. For the PGMFI this module is used for signal amplification, carb'd application is only the diode as you discovered. reed switches or relays in this kinda DC setup will produce a "square wave" ,not a literal clean waveform if you observe the signal on a oscilloscope as you will have "bounce" or noise as the switch closes.

also another little hint: put a multi meter on the back two screw terminals and spin the speedo like the cable would..... 4 pulses per 1 revolution

[lostforawhile]

silk screen marks can be used as indicators, there are a few resistors, capacitors, zener diodes and a triode. For the PGMFI this module is used for signal amplification, carb'd application is only the diode as you discovered. reed switches or relays in this kinda DC setup will produce a "square wave" ,not a literal clean waveform if you observe the signal on a oscilloscope as you will have "bounce" or noise as the switch closes.

also another little hint: put a multi meter on the back two screw terminals and spin the speedo like the cable would..... 4 pulses per 1 revolution

I've got one that shows one pulse per revolution and one that shows four, both the plastic covers are different, maby a small difference between models,who knows, the voice warning system from the Z doesn't care, it's just a signal that the car is in motion as far as it goes

[gp02a0083]

I've got one that shows one pulse per revolution and one that shows four, both the plastic covers are different, maby a small difference between models,who knows, the voice warning system from the Z doesn't care, it's just a signal that the car is in motion as far as it goes

Couldn't care about that "Bitching Betty" warning system as it does not function for anything other than the doors, low fuel level, parking brake, key in ignition and lights. Otherwise mention of this system is a non stock part and outside of the scope of this discussion.

Now to get this discussion back on track again.
As far as the module on the back of the cluster both the ND and NS versions both have just a diode box for the carb'd models and the same board used for the PGMFI for signal amplification. Location of the ND plug is horizontal and on the bottom vs the Seiki type is vertical and of to the side. The picture you displayed is most likely a Seiki type from a non PGMFI car and from the part # the two beginning letters are NS . You might want to double check that speedo, factory manual spec is 4 pulses per 1 revolution.

Now on the reed switch, they are pretty robust and really the two main sources of failure for those kinda devices is a cracked capsule allowing air and moisture to alter the contact properties and open/close characteristics. The other is using too high of a potential and current that ends up producing unwanted arching. With that being said if used properly they can have been known to have decent lifetime cycles into the billions depending on design. Without any additional circuitry, using a simple power supply,resistor, reed switch and magnet you can obtain a waveform similar to this ( note additional components could be used like capacitors and zener diodes to clean signal up more):

bump for Dr. Snooze, here is your pulse generator you asked about ok, this looks to be from an LX, as the LXI wiring diagram shows a power wire going into the speed sensor amplifier, but it also shows three generic marked grey wires from the speed pulser, which dont actually exist, did the JDM versions of these cars come with an actual VSS instead of a cable? I wonder if the LXI speed sensor amplifier has an actual 5 volt square wave output? someone needs to hook one to a scope if it does, that could be useful to a lot of people

I'd like to see that factory schematic, as far as I can see the only wires to the speed pulser is the one wire in from the cruise control unit and a ground wire. The speed sensor amplifier only have a power wire that is fed off of a 15A fuse, a ground wire and a output wire to the PGMFI / solenoid control unit. Schematic found on 25-50

[lostforawhile]

Couldn't care about that "Bitching Betty" warning system as it does not function for anything other than the doors, low fuel level, parking brake, key in ignition and lights. Otherwise mention of this system is a non stock part and outside of the scope of this discussion.

Now to get this discussion back on track again.
As far as the module on the back of the cluster both the ND and NS versions both have just a diode box for the carb'd models and the same board used for the PGMFI for signal amplification. Location of the ND plug is horizontal and on the bottom vs the Seiki type is vertical and of to the side. The picture you displayed is most likely a Seiki type from a non PGMFI car and from the part # the two beginning letters are NS . You might want to double check that speedo, factory manual spec is 4 pulses per 1 revolution.

Now on the reed switch, they are pretty robust and really the two main sources of failure for those kinda devices is a cracked capsule allowing air and moisture to alter the contact properties and open/close characteristics. The other is using too high of a potential and current that ends up producing unwanted arching. With that being said if used properly they can have been known to have decent lifetime cycles into the billions depending on design. Without any additional circuitry, using a simple power supply,resistor, reed switch and magnet you can obtain a waveform similar to this ( note additional components could be used like capacitors and zener diodes to clean signal up more):





I'd like to see that factory schematic, as far as I can see the only wires to the speed pulser is the one wire in from the cruise control unit and a ground wire. The speed sensor amplifier only have a power wire that is fed off of a 15A fuse, a ground wire and a output wire to the PGMFI / solenoid control unit. Schematic found on 25-50

as soon as I find my book in here I'll see if I can get my scanner working, it shows three generic wires with no color codes coming from it, thats why I wondered if that was some kind of carry over from the jdm cars

[gp02a0083]

as soon as I find my book in here I'll see if I can get my scanner working, it shows three generic wires with no color codes coming from it, thats why I wondered if that was some kind of carry over from the jdm cars

I doubt its a carry over, considering the lack of color codes on a cluster. Also it does not appear on the RHD version of the schematic that is on the next page from the LHD schematic.....