Megasquirt MSEXTRA and MS3EFI support forum

by **racingmini_mtl** » Sat Jun 10, 2006 6:08 pm

Following the development of the hi-resolution MS1/extra code and for a future version of MS2 code (and MS3?), I have designed a small daughterboard that has 4 peak and hold injector drivers.

Since the hi-res MS1/extra code can't do a PWM signal on the injectors, the only solution with the standard MS injector drivers is to either use hi-z injectors or use inline resistors. This board allows the use of low-z injectors without any resistors and without setting up any PWM parameter since the chip (LM1949) the board is based on takes care of setting the current correctly no matter what the battery voltage is or what injector is there.

However, these drivers can only handle a single injector so the board can be used for engines with up to 4 injectors. For more injectors, more boards can be used.

I've designed the board such that there is one input per driver so each injector can be controlled by either of the 2 available MS injector channels (and this will allow 4 independent injector channels in the future MS2 code). Also, there is a single active flyback circuit for the 4 drivers as per Bruce's recommendation. The board layout assumes that the board will be used in either the lowest or the highest slot of the standard MS case with the 5 TO220 transistors bolted to the case. The initial board measures 4" by about 1.1" which means it should fit well in the case slot and be short enough to allow more than one board to be used. I still need to verify those measurements. The current BOM comes up to about $40 to $50 at Digikey but that does not include the board cost. However, if you are building a new board, all the injector driver parts are no longer needed so there could be some cost reduction there.

So, if there is some interest I could produce such a board. I would confirm everything before having the board made. I could also organize a group buy for all the parts needed. To have a significant reduction in price, the group buy would need to be for at least 25 boards. If there is no interest in the group buy, a smaller batch of boards could be done but the fewer boards made the higher the cost per board is.

So, let me know if you would want to buy such a board, how many boards you'd want, and if you would be interested in the group buy. I have attached the schematics of the board. Also, let me know if you have comments on the schematics.

Jean

by **mitsuko** » Sat Jun 10, 2006 10:03 pm

In the lm1949 datasheet , they reccomend using a double sided , but not plated trough board .
This way you can route the high injector current to the bottom layer , and the current sense trace to the lm1949 on the top layer .
Both layers soldered separatly to the current sense resistor .

Did you implement that on your board ?

Pat

by **racingmini_mtl** » Sun Jun 11, 2006 6:40 am

The datasheet says that the sense resistor should be Kelvin connected and one way to achieve that is the way you mention.

I have not done this for 2 reasons: first it is more expensive to have board made with unplated holes and second, I wanted to have the board small to easily allow the use of many boards and to reduce cost. However, I did make sure that the trace going from pins 4 and 5 to the sense resistor do not carry any high current (or other signals) and that pins 4 and 5 are only connected to those traces.

If you think that the sense error will be too important with this method, the board could be made slightly larger and the sense resistor mounting holes could be drilled to remove the plating. I'm just wondering if the precision needed warrants that effort especially since sloppy assembly could be a more important error factor.

In any case, thank you for the comment and let me know if you have anything to add.

Jean

by **racingmini_mtl** » Mon Jun 12, 2006 9:57 am

I did a small modification to my layout and the sense signals are now on the top layer and the high current traces are on the bottom layer. The only thing would be the need to drill out the hole plating for the current sense resistor before assembly and solder the resistor to both the top and bottom layers. I would be curious to see how much difference it actually makes in the precision of the peak and hold currents.

I also had a quick look at prices and if i could get a group buy of 25 or more, the price of the board would pretty much be covered by the volume savings for the parts. So it would be about $40-$50 per board for parts and board.

Jean

by **Brad-Man** » Sat Jun 17, 2006 9:59 pm

I'm in for two...gee-I'm finally first at something!

by **EstateAgent** » Sun Jun 18, 2006 5:09 am

How does this differ from the flyback board available at the moment?

by **racingmini_mtl** » Sun Jun 18, 2006 6:24 am

The flyback board adds the flyback PWM damping circuit that is included on the V3 board. This board (Peak & hold driver board) actually replaces all the injector driver components on either the V2.2 or V3 board. It also frees the PWM processor pins on MS1. MS2 would need some hardware modifications to get back the PWM pins.

You should have a look at the LM1949 datasheet to give you a better idea of the function of the board. http://cache.national.com/ds/LM/LM1949.pdf

Brad-Man, are you interested in the board only or in the group buy? As soon as I have interest for 10 boards I can have a small batch made or if I get interest for 25 boards in a group buy then we can have it. Or course if we have interest for more boards only, then the cost gets lower.

Jean

by **71jeep** » Sun Jun 18, 2006 9:19 am

I would be in for one.

Thanks 71jeep

by **EstateAgent** » Mon Jun 19, 2006 2:05 am

I may just be interested in a board

So let us know a rough price. (take PayPal?)

Tried sourcing the LM1949's, just seeing if National will let me have some freebies :lol:

by **racingmini_mtl** » Mon Jun 19, 2006 12:23 pm

A rough estimate would be about $18 per board if we can get enough interest for 10 boards. Shipping would be extra but should be quite small since this would easily fit in an envelop. I would be able to take Paypal but might have to pass along their cost (3-5%?)

I have attached the BOM with digikey part numbers and price.

Jean

by **EstateAgent** » Tue Jun 20, 2006 2:12 am

Sounds good. Definately interested

I presume we can tie 2 inputs together (i.e pin 1 of U1 and pin 1 of U4 and same for other 2).

by **racingmini_mtl** » Tue Jun 20, 2006 9:04 am

EstateAgent wrote:I presume we can tie 2 inputs together (i.e pin 1 of U1 and pin 1 of U4 and same for other 2).

Yes, that's what you'd need to do for a 4 cylinder engine. You could either run a jumper on the board or tie wires together off the board.

by **Brad-Man** » Fri Jun 23, 2006 3:16 pm

My # 1 prefernce would be aq group buy of all parts including board for 2 boards, since I have a 6 cylinder engine.

If not enough people are up for the remaining 23 kits for the group buy, then I guess I'll have to just go with the boards...There are a few things I can order from Digikey in addition to this stuff to make the hadnling charge not obscene...but I've lived without'em for this long.

I can't imagine that there wouldn't be more interest though....

PayPal is cool buy me with the 3% added....

by **Brad-Man** » Mon Jun 26, 2006 4:56 pm

As a matter of fact, I'm in for 4 boards &/or kits, since I have 2 projects I'm building for....

by **racingmini_mtl** » Mon Jun 26, 2006 5:50 pm

Well if I can get 1 or 2 more interested in a board then I can get them made. If that happens I'll contact everyone who showed interest to confirm if they're still interested and post here when I get confirmation that I have the required number.

Jean

by **Brad-Man** » Thu Jun 29, 2006 10:03 pm

racingmini_mtl:

I'll be a sport and say I'll ante for 6 boards.

If you find people that want the 2 extra I will spring for between now and when they come in, just send me back the money, or maybe parts....

Sound fair?

What do I do to get money to you?

by **racingmini_mtl** » Fri Jun 30, 2006 7:34 am

Brad-Man,

Thanks for the offer but you don't have to do that. I also want to have some soon so I'll have the boards made now and I'll have enough for those who said they were interested plus a few spares. At best I'll sell all boards and make another batch, at worst I'll have some spares that I know I'll need later.

My Paypal address is racingmini_mtl at yahoo.ca. For 4 boards that's $72 plus $5 for shipping and Paypal fees. The Canada Post web site makes it very difficult to find how much it would be but if I send it as a small package, that's about 5 canadian$ so the US$5 should cover shipping and part of the fees. The boards would fit in an envelop but I'm not sure how they would survive the trip.

If that's fine for you, PM me your address and a note that the payment has been made.

For the other people,

The $5 shipping + fees should be the same for everyone in the US for 1 to 4 boards. Once I have the boards, I'll see if I can do better at the post office but for the moment that's what I'm confortable with. So if you're still interested, you can send your payment and PM me your info.

Jean

by **Brad-Man** » Fri Jun 30, 2006 8:42 am

Have sent money and have PM'd you.

by **racingmini_mtl** » Fri Jun 30, 2006 10:13 am

Brad-Man, you have a PM.

by **Joethemechanic** » Sun Jul 02, 2006 2:31 am

This is cool!

So am I to understand that the hi res extra code is now stable?

If so would you recomend using this board/code option on a 2.2l 4cyl. with 750cc injectors?

I am thinking that it would be a good idea just to have it anyway if the price is resonable.

can I still get in on a group buy?
Thanks Joe 2.2l honda V3 MS&Se 029q

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