Many questions about how to build a MIMA_L

[RobertSmalls]

I'm a mechanical engineer, and I have previously been happy to leave electronics to the electrical engineers, but I'm going to assemble a MIMA_L. I have the schematic, which has part numbers on all the parts. Though there are a few surprises, such as one TLC2272 provides two op-amps. Do I likewise need only one 74C221A?

I checked out the examples at DIY MIMA L - MIMA Honda Insight Modified Integrated Motor Assist, but there are a few things I'm not sure about yet:

*I plan to add FAS and CARD to the same board, or an adjacent board. How large of a board will I need?
*What kind of breadboard should I order? Fiberglass or phenolic, and how thick?
*Did JoeCVT just use blobs of solder instead of wires between all of the IC's and discrete components on the breadboard?
*There are three rheostats, which I believe are controls presented to the user, though I don't know what VR3 does. Where can I buy suitable joysticks, hand throttles, control knobs, etc?
*I don't like any of my options for cutting into the ECU wire harness. I guess I'm going to use 16 conductors of a ribbon cable for the wires that need to pass through my circuit board, and 8 conductors for wires that need to be teed to my board. For the former, I was going to cut, strip, and solder the wires together, then wrap with electrical tape. For the latter, is there anything better than solderless inline splices?

Thanks in advance for helping me improve my circuit building skills, and I'd especially like to thank Mike Dabrowski for developing IMA mods. Mike, I'll mail you a portion of the gasoline I save as a thank you.

Robert

[3-Wheeler]

Hi Robert,

The joystick pot is: (used for VR1)

Digikey part # 252A103B60NB-ND

They may be out of stock, so you may have to pick a similar one of another part number.

You will also need a 2kHz square wave for "tuning" the RC networks. Since I don't have a frequency generator anymore, I was planning on using a sound card and audio amplifier for generating this signal.

You will also need either an oscilloscope or multimeter with a duty cycle function. I don't have a meter like this myself, but I can borrow one from work to accomplish this.

Check out this:

MIMA for CVT

There are three pages of very good information here. Mike gives a very clear explanation on how to go about this.

Whoops, almost forgot.

Pin #5 of U1B on Mike's schematic is currently shown unconnected. Usually these floating pins should either be referenced to ground or pulled to VCC (+5VDC). It would be nice to find out where this should be pulled.

__________________________________________________ _____

I would like to find out what type of connector to use for splicing into the harness wiring. I have not looked at the wire size to determine if a 9-pin D connector would suffice for this application. According to Mike's schematic, that would cover all the wires that are used.

If a male/female combination is used, then in the event that MIMA is removed from the car, the two original connectors can be reinserted and bring it back to original condition.

I know JoeCVT used much larger connectors. Maybe for ease of installation?

Jim.

[joecvt]

Originally Posted by RobertSmalls

*Did JoeCVT just use blobs of solder instead of wires between all of the IC's and discrete components on the breadboard?

Blobs of solder.....I prefer to call it a rugged design without any wires that may work loose Actually, I used this 750 hole board from Radio Shack:

Grid-Style PC Board with 750 Holes - RadioShack.com

Each hole has a pad (none are connected on this board). I used thin wire and solder to make the traces to each component instead of wire going to each component. I wanted to make a small footprint so the board that I used is close to the size of the Insight car key. I also added some circuitry for the foot pedal and auto activate that required some rework so the job became a bit more messy (over all looks) but it still works after several years of use in hot and very cold climates

In my newer design in the future, I may attempt to use those chemical etching boards.

JoeCVT = Just your average CVT owner

[joecvt]

Originally Posted by 3-Wheeler

I know JoeCVT used much larger connectors. Maybe for ease of installation?

I had both connector ends with wires attached already on-hand. It is really the same power connector that you would plug into a disk drive. This was a very early MIMA_L build (I think the 3rd or 4th ever built) and I didn't think to use ribbon cabling. It is also the first MIMA_L that uses a foot pedal with auto MIMA activation instead of a hand controlled joystick.

Also, it was easy for me to make a single loopback connector for cmdpwr and mamod1 that I still carry in the coin storage just in case of a malfunction. I have cmdpwr and mamod1 using the same 4 pin connector. The other 4 pin connector is for the foot pedal (replacing the joystick) and mamod2. The smaller connector is a floppy power connector and it is used to supply power to the MIMA_L board.

In case you haven't noticed a pattern of some parts I used, I have some old PCs laying around.

JoeCVT = Just your average CVT owner

[MN Driver]

Joecvt, I always wondered how those grid boards were soldered, I didn't realize that people were using thin wire against the board and then soldering it down. I wasn't taught how those worked but it's good to know. I know from experience that jumping gaps isn't easy but never really thought about how that was done.

When I learned electronics, whenever making my own PCBs I've always used the ferric chloride method but I don't use trays any longer. I wet a sponge with ferric chloride and then 'rub' the surface and it is amazingly quick and I don't have to worry about a full tray of 'toxic fluid' that I need to recollect for reuse. A bottle of the stuff lasts a very long time even with a great deal of use this way. I still use the pressure donuts and PCB tape, although I've come across clever ways of printing with a laser printer on some form of thermal transfer paper but I guess I'm old fashioned and I do it manually. ...and of course drilling, I drill the little holes with a thin nail that I've sharpened and tapered the point on and that seems to work well versus trying to find an adequate bit.

[joecvt]

I have read about the laser print and rub method but I don't have a laser printer. I have read about another type of blank board that is sensitive to fluorescent light. You print your layout on clear transparency film, align the just printed layout with blank board, place a piece of glass on top, put it under the fluorescent light for about 15 minutes then do the chemical stuff....That may be the way that I go if I make another MIMA_L with some improvements.

JoeCVT = Just your average CVT owner

[Mike Dabrowski 2000]

I drove around for months with just an experimenters board version, until I built the first MIMA-C computer system. Over the years I have made many breadboards that became parts of machines, and are still working after 15 years.
as long as you keep dust and moisture out they can last for many years.

http://www.99mpg.com/mima/diymimal/m...rd_small.jpg,0

Soldering the parts to a plated through .1" on center perf board like this.
Jameco Electronics Electronic Design: JAMECO VALUEPRO: PCB-7038-R
Is another way to make a very sound circuit board, you layout the parts in the holes, trying to optimize the positions based on what other parts are connecting to it. Once you like the main part layout, you solder in all the parts. Finally you use insulated 22 Gage solid wire for the jumpers, Strip only 1/8" from each jumper end and solder carefully. Resistor and capacitor leads can form heavy buses if soldered to the board. TIP, just before you start making the pc board,take some fine steel wool or scotch brite and buff the surface of the perf board to make the copper shiny. Blow or brush off any steel wool fragments. This clean copper surface will make soldering easy. If you use old resistors, you may want to buff the leads if solder does not flow easily.
Use only temperature stable capacitors for the RC time constants, and use 1% tolerance high quality resistors. This will assure that MIMA L will be stable over wide temperature swings. The last thing you want is for there to always be a little assist or regen running.

I buy large boards and cut out the board size that works for the circuit.

In theory one could build a MIMA L with a built in joystick on one board that would only need a multi conductor wire to connect to power, ground, and the other IMA signals.
This whole board joystick assembly could be epoxy covered to become a new stalk on the steering column? or bump on the e-brake? use your imagination. McMaster-Carr
Have Fun

[02insight]

What is this tuning RC Networks for? Without this MIMA_L cant work?

Originally Posted by 3-Wheeler

You will also need a 2kHz square wave for "tuning" the RC networks. Since I don't have a frequency generator anymore, I was planning on using a sound card and audio amplifier for generating this signal.

You will also need either an oscilloscope or multimeter with a duty cycle function. I don't have a meter like this myself, but I can borrow one from work to accomplish this.

[Mike Dabrowski 2000]

I just took another look at my MIMA-L schematic.
I see that there are a few areas where people could get confused.
The ONE shot U1A 74HC221 is the same part as what I call U1B a 74C221.
The HC operates at 5V, the C version operates up to 12V.
Either part will work fine.
Notice that U1A and U1B use different pins for the same function. This is because U1A and U1B are different sections of the same Dual one shot chip.
U1A is triggered by the cars 2khz pulse, so R1, VR1, and C2 will determine how long the pulse is produced. You want the midpoint in the pot(spring return to center) which will be ~5kohm on a 10K pot to produce a pulse that stays high for 50% of the 2Khz. You will need this to be as close to that 50% point as you can by adjusting the value of C2.
You will need an accurate source of the triggering 2khz pulse, and an oscilloscope to see the relationship of the one shot pulse to the total 2KHZ.
The other half of U1 works in a similar way.
The MAMODE 20 KHZ pulse from the car triggers U1B, and VR3 and C1 determine how long the pulse will be high after each 20KHZ pulse.
A LM555 can be used to generate both the 2KHZ and the 20 KHZ pulse(different resistor value) you need some way to accurately measure the 555 output frequency or the one shot duty cycle will be incorrect.
This tuning will change if the capacitor or resistor changes value with temperature, therefore the need for temperature stable caps and resistors in the two timing circuits.
LM555 Timer Circuits
You can use the circuit shown as astable oscillator, and the resistor/capacitor to frequency calculator will get you close to the values required for 2khz and 20 khz.
Set the circuit to make a 2khz square wave, and use that to trigger U1A, once you confirm that you can get 10% to 90% dutycycle with the joystick, change the values on the 555 to get a 20 khz square wave, and tune VR3 on MIMA l to get the 25% dutycycle.

[3-Wheeler]

Originally Posted by 02insight

What is this tuning RC Networks for? Without this MIMA_L cant work?

Thanks Mike for the additional information on MIMA_L.

Just wanted to mention for those that are not familiar with passive components...

When Mike is referring to 1% precision resistors, these are typically known as "metal film" resistors. These are more stable over the long term than carbon film resistors.

For capacitors, stay away from electrolytic or ceramic for this application. Polystyrene is probably the ideal capacitor, but these tend to get large and expensive in the capacities required for this application.

Mica, or polyester are also stable types, and JoeCVT mentioned in a separate posting that he used polyester with good success for his MIMA_L board.

Jim.