Your Projects

Originally posted by MIPS 11-09-2019

Here's the general idea for the two 74x48mm panels that hold the labels.

Originally posted by MIPS 10-31-2019

At this point here the project is complete, aside from labeling all the indicators.
Initially the idea was to use Letraset or silkscreening, but found out that was impractical for how small the text needed to be. Now I'm thinking two metal plates with the lettering etched on it and then glued down. Problem is that I don't have experience with the laser to lay out and align the text. Would anyone be willing to assist in this last step? I can measure out everything no problem.

Originally posted by MIPS 06-28-2019

The modification is completed and tested.

This technically is now a custom IC. +12v enters and is regulated and filtered locally and all you have to do is feed it the output of the O2 sensor. and you get a suitable output for the meter. Because of the 1 megaohm resistor (used to load the input in the case of intermittent connections) however the O2 sensor signal is dampened by 0.1v which is unacceptable normally but for the purpose of diagnostics is acceptable. IF a solution to his is created at a later date however it's as simple as pulling the module and reworking it.

Originally posted by MIPS 06-29-2019

A solution to the O2 sensor meter problem is an op-amp buffer.
https://electronicsarea.com/op-amp-voltage-follower-buffer/

This circuit is a Op-Amp Voltage follower (Buffer).

The buffer has an output that is exactly as the input. This behavior may initially seem useless, but has features that help solve impedance coupling problems.
The input impedance of a buffer with an operational amplifier is very high, close to infinity
The output impedance is very low, just a few ohms.

If the input impedance is very high, it does not charge the circuit that is sending the signal, and if its output impedance is low, it can deliver a sufficient amount of current to the circuit receiving the signal.

In other words a Buffer requests very little current from the circuit that gives the signal and greatly increases the capacity to delivery current to the circuit that receives the signal.

Because the relay board does not take up much space and everything terminates through their own connections, adding this circuit is as easy as adding in a second board. The circuit at its basics uses an LM358 op-amp however because we do not have 5v locally available form the car an additional power supply circuit consisting of a 7805 and filtering capacitors will have to be added after the power switch to convert the 13-15v input to a regulated 5v output.

Originally posted by MIPS 06-27-2019

A new problem has surfaced.
Now that a working O2 sensor is present in the car, the verification process found that AMC mandated any test equipment attached to the sensor wire have an impedance of 1 megaohm or more. The 1v voltmeter I selected has a 1K winding resistance and unlike the other sensor outputs, this is directly tied to the sensor. The result is that the meter acts like a 1K pulldown resistor and biases the O2 sensor reading sent to the computer, resulting in an inaccurate reading by forcing it to always be far leaner than it actually is. Somehow I need to figure out a way to isolate an analog signal with a very low voltage, otherwise that makes two meters that don't really work.

Originally posted by MIPS 06-11-2019

Hmm, a problem has developed.

I forgot that a standard RPM meter will display speed as one pulse per revolution. On the Eagle and similar vehicles, if you are pulling the RPM from the ignition TACH signal as opposed to a crank or cam position sensor you are receiving multiple pulses per rotation. One for each firing instance to the coil. Running the meter on this results in the RPM, multiplied by six, so if you are idling at 600RPM the display will show 3600RPM, which is the redline for the 258.
The RPM meter however that I chose includes some form of a ratio divider that it gives no specifics about. You can also toggle between acting as an RPM meter or a frequency counter, so that should fix the multiple issue, right?

Not quite. For reasons I do not yet understand this otherwise accurate RPM meter has a variance of 300RPM in either direction. For a device that should be off by no more than 50RPM that puts it far into "unusable". Likewise while the division takes place, display refreshes will continue at the input pulse speed and not at the divided speed, or six times faster than we really need it.
The result is a display that can vary wildly as it flashes numbers.

An intermediate circuit that conditions and divides the TACH before it reaches the meter may be necessary.

Originally posted by MIPS 06-09-2019

Progression. Now the single-state LEDs (altitude jumper and the two motor phases) and the red LED's are wired in.

Keep in mind that the inputs from this side of the diagnostic connector are not loaded. The optoisolators do not enjoy floating inputs and can on occasion sporadically fire when touched or the input power is unstable. Pullup resistors are provided inside the computer for this purpose and adding more over here may interfere with the computer, plus the diagnostic unit can only work when plugged into the harness anyways so normally it won't matter.
the other issue I've discovered is that my desk is contaminated with some sort of fine and conductive metallic dust that is getting into the flux and causing high resistance bridges. The board will have to be extensively cleaned or else recurring glitchyness will happen.

Originally posted by MIPS 06-03-2019

It begins to show signs of life....

Tonight was wiring together the "A-Bus" which is mainly signal inputs, plus meter connections. All wiring is point-to-point soldering.

B-Bus and C-bus are mainly the lamp outputs, arranged so that positive voltages are only on even pins while the negative (or ground) are odd pins and thus you basically solder together one row of pins and bam, grounds are done.

Originally posted by MIPS 05-28-2019

A few people might of seen it on Saturday.
The unit required some additional research to verify it would work. This required as part of another project to reverse engineer the computer completely for conversion to an arduino device to source another computer, depot it and do a little reverse engineering to see how exactly the signal ground worked when the computer itself is well noted in documentation to NEVER be put in contact with chassis ground.
I won't go totally into detail as to what I've done and how but here's pretty pictures for the moment.

Edited: Nifty. The depotting process was documented by me on another forum however I submitted it to Hackaday and it was posted on the 27th.

Originally posted by MIPS 05-04-2019

Work resumes.

The cabling harness had to be rebuilt due to pin errors discovered during assembly.

The cable was made as a separate piece due to AMC and later Chrysler/Jeep continuing to use the same diagnostic connector, but with a different pinout. This way if you need to use the box with another unit it only requires a different harness.

Originally posted by MIPS 02-18-2019

Last night consisted almost entirely of preparing for the one thing I was not looking forward to: Making the connections.

This PCB is what controls all the lights and distributes EVERYTHING. The ten relays operate the red/green lamps for the more important sensors. Each relay has a diode for the flywheel and the board will consist of ten of the above circuit, plus potentially a bit more space in case I need to add tweaks for the tach-to-tachometer signal. While the two rear connectors are hardwired to the plugboard everything else passes through three 26 pin connectors. Just preparing everything for the soldering took a significant portion of the night.

I'm still not done. There's another 26 wires left and in the process I found out I screwed up the pinning on the rear connectors, so that harness will have to be dismantled and de-pinned form the molex plugs and done again. I'm exhausted. I'm done for today.

Originally posted by MIPS 02-06-2019

Another circuit idea is the use of relatively inexpensive 4N33 optoisolators, as demonstrated below:

Edited: Because I am using 12V relays with exceptionally low coil current (30ma) you can actually rather safely drive the relay directly from the optoisolator. An even simpler circuit is the following:

Where the transistor is the output side of the 4N33. The reason I would suggest this way is that it closely reflects an earlier diagnostic unit someone else made in that the computer inputs and outputs do not mind the very light load of an LED but we can still isolate the entire diagnostics system from the computer in case a catastrophic failure occurs.

Edited: Edited: And here is the above breadboarded. The only selective component is the 680 ohm resistor which will let me not blow out the optocoupler in the unwieldy 11v-14v DC range a car will run on. The orange wire is what you would have tap into the diagnostic connector.

Originally posted by MIPS 02-05-2019

Aaaaand the exterior is all done up. Looks sharp!

Now of course that leaves us now with the internal wiring to complete. That will wait until the MOSFETs arrive. In the meantime I still do not know how to put down the labels for each indicator. It's too small for vinyl and I don't remotely have the supplies to silkscreen.

Originally posted by MIPS 02-02-2019

While I work on the enclosure I am seeking a bit of external help on how to make all the lamps work.
the original design for an aftermarket diagnostic unit is here however is in comparison a far simpler device where a series wired resistor and LED connect to each computer input/output. My box as seen above has two lights to represent each sensor. That way I can better identify when something is opened or closed. To do so requires a dual position relay for each lamp. That however means that the computer then needs to deal with a 33ma current as opposed to something like 3ma from an LED and you have a connection to ground through the coil which may also interfere with the computer. The solution is to use a MOSFET or a darlington pair set of transistors to isolate the CeC control circuit from the lamp switch circuit.
Initially I was working on salvaging parts from a shift register controlled 16 relay security module.

This however did not work when breadboarded, partially because I reverse engineered the original circuit wrong. When I referred to a friend his suggestion was to scrap the darlington pair entirely and use something like a 2N7000 MOSFET.

I will have to purchase the parts and wait for them to arrive before proceeding with additional testing.

Originally posted by MIPS 01-24-2019

Transferred out the holes and openings form the layout to aluminum sheet and then after center punching and pilot drilling we got the metalwork finished.

Up next is widening all the holes to fit their designated lights and switches. Still unsure how to apply the labels.

Originally posted by MIPS 01-14-2019

The box arrived. It's tight. A little bit smaller that what I wanted but there were no other affordable options available.

The meters need to be trimmed slightly so that they will mount properly to the top half. There's a circular indent in the back which serves no purpose and couldn't remain or else the aluminum plate would be too thin at the top and bottom and prone to breaking. Removing the indent gives me 50% of the material for strength.


I will be in on Wednesday to try and get the drill holes for the plates marked out. I'm hoping I only need to do this ONCE.

I also marked out where the harness comes into the box on the back. A metal plate lives on the inside to reinforce both connectors as one assembly.

Originally posted by MIPS 01-04-2019

Sat down tonight and drafted the layout for the panels.

Meters mount on the upper panel with the digital tachometer in the middle. The lower panel has the red, green and yellow indicator lights on the left and right sides (plus the power switch) with an electrically identical arrangement of banana plugs in the middle for jumpering or additional metering of the pins directly from the diagnostic connector.
Remember that all the indicators operate either on or off. Each red and green LED operates with a relay between the lamps and the pin on the diagnostic harness. The two large connectors that connect the box to the harness stick out the back and the entire unit is protected by a fuse on the +12v pin.

Some highlighting will be done...somehow. Either paint or cut vinyl. Lettering...I dunno but I'm not doing it by hand.

Originally posted by MIPS 01-01-2019

After some procrastinating I decided to buy one of the double sloped enclosures seen above, albeit it is coming from the UK for $50 shipped.

https://www.ebay.ca/itm/141895697839

It is not however coming with the aluminum panels that you mount your components to. I know we have some sheet at the makerspace still, would anyone be able to help me by cutting out two pieces in the following dimensions?

248 x 99mm
248 x 49mm

Failing that it shouldn't be too hard to quickly cut out two pieces of acrylic.

Originally posted by MIPS 12-18-2018

This is the wire harness I spent the last two Hack Nights assembling and repinning. The Molex plugs and pins were purchased at RTS electronics and cost about $7.

This is most of the components for the Diagnostic Unit. The 12v relays are still in the mail.
The items purchased can be (or could be) found below:
https://www.ebay.ca/itm/85C1-V-Pointer-DC-Volt-meter-Panel-meter-Class-2-5-1V-5V-10V-20V-30V-100V-500V/162194309857?ssPageName=STRK%3AMEBIDX%3AIT&var=461168023277&_trksid=p2060353.m2749.l2649

https://www.ebay.ca/itm/5Sets-Lantern-plug-4mm-banana-plug-Jack-socket-experiment-connection-test/162491943130?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

https://www.ebay.ca/sch/sis.html?_nkw=4%20Digital%20Motor%20LED%20Tachometer%20RPM%20Speed%20Measure%20Gauge%20Meter%20Tester%205%209999&_itemId=202444043494

https://www.ebay.ca/sch/sis.html?_nkw=10%20Pcs%20lot%20Electric%20Appliances%20SRD%2012VDC%20SL%20C%20Mini%205%20Pins%20Relay%20Normally%20Open&_itemId=232788867491

https://www.ebay.ca/sch/sis.html?_nkw=6mm%206%2012V%20Car%20Truck%20Boat%20Metal%20LED%20Indicator%20Pilot%20Dash%20Light%20Lamp%20Wire%20Leads%20JB&_itemId=263526100743

The fuse holder was something random I found in the Hack Room as well. The Gould WindoGraf machine will make an excellent piece of secondary equipment for monitoring circuits over a prolonged period of time however requires sufficient transient supression and can only monitor four channels at a time.

Originally posted by MIPS 12-18-2018

Regrettably due to a number of expensive upcoming major repairs that will be needed I have decided to retire my '92 Geo Tracker after ten years of reliable service sometime this spring. In it's place it makes sense I bought something older. A 1982 AMC Eagle.

This car existed in the VERY very early days of computer emissions control and at the tail end of emissions systems of the 70's that really strangled engines to keep smog down. The 6-cylinder engine in the Eagle uses a number of digital sensors and a stepper motor attached to the Carter BBD dual barrel carburetor which on its own seems to be the scorn of most old farts because how dare a computer do the lord's work in a carburetor!
Anyways the major issue with these configurations is that when something fails the computer does not tell you. The 4 and 6 cylinder Computerized Engine Control (CeC) does not utilize a Check Engine light or any method to store codes on the 6-cylinder model. It just assumes everything works, otherwise the car runs like crap. The computer itself is encapsulated in potting compound. If I can find another of these computers I would like to take a shot at stripping the potting off to reveal exactly what is going on inside this.

This car existed in the VERY very early days of computer emissions control and at the tail end of emissions systems of the 70's that really strangled engines to keep smog down. The 6-cylinder engine in the Eagle uses a number of digital sensors and a stepper motor attached to the Carter BBD dual barrel carburetor which on its own seems to be the scorn of most old farts because how dare a computer do the lord's work in a carburetor!
Anyways the major issue with these configurations is that when something fails the computer does not tell you. The 4 and 6 cylinder Computerized Engine Control (CeC) does not utilize a Check Engine light or any method to store codes on the 6-cylinder model. It just assumes everything works, otherwise the car runs like crap. The computer itself is encapsulated in potting compound. If I can find another of these computers I would like to take a shot at stripping the potting off to reveal exactly what is going on inside this.

This car existed in the VERY very early days of computer emissions control and at the tail end of emissions systems of the 70's that really strangled engines to keep smog down. The 6-cylinder engine in the Eagle uses a number of digital sensors and a stepper motor attached to the Carter BBD dual barrel carburetor which on its own seems to be the scorn of most old farts because how dare a computer do the lord's work in a carburetor!
Anyways the major issue with these configurations is that when something fails the computer does not tell you. The 4 and 6 cylinder Computerized Engine Control (CeC) does not utilize a Check Engine light or any method to store codes on the 6-cylinder model. It just assumes everything works, otherwise the car runs like crap. The computer itself is encapsulated in potting compound. If I can find another of these computers I would like to take a shot at stripping the potting off to reveal exactly what is going on inside this.

Only the O2 sensor exists as an analog input. Once heated it will vary between 0 and 1v to inform the CeC if the engine is burning too rich or too lean and that in turn allows the CeC to step pins inside the carburator to adjust the air/fuel ratio.


This project consist of three phases, each progressively more complicated:

-Add test pin for O2 sensor to the diagnostic harness, which is easy as the 6-pin Molex has four unused pins
-Assemble wiring harness to connect vehicle to the Diagnostic Unit. I know we have the parts needed in the Hack Room
-Assemble the Diagnostic Unit

The Diagnostic Unit requires no logic. If a solenoid is on, an LED lights. If it's not, the LED goes out. As an extra feature for switches I can use a relay driven by the sensor to toggle indicator lights to show if something is opened or closed. Battery and O2 sensor readings can be read using regular analog meters. A 1 and 15V meter respectively are perfect. Engine RPM can also be monitored using a digital tachometer. Additionally the Molex Plugs can be represented with a group of banana plug sockets to aid in diagnostics where signals must be forced by grounding or adding voltage to a line. The whole assembly fits into a sloped enclosure, presumably of plastic. I have two ideas in mind for what to buy but it comes down to finding one at the right price. Hobby enclosures seem to get really expensive once you want more than just a box. Nobody in town sells enclosures this complicated that I have found and Lee's Electronics in Vancouver does not have boxes large enough in plastic.