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sorry this is my first post on this forum. I've spent a fair while combing the internet looking for advice and have not been able to find any information.

The problem: So I've converted the engine in my bmw e30 to a 6 cylinder engine from a 4 cylinder engine and the tacho for the instrument cluster is reading incorrectly. It is to my knowledge that the signal needs to be multiplied by 3/2 to achieve an accurate result. Originally my plan was to implement some kind of frequency divider to achieve this. However, I found out that the coding plugs for 6 cylinder cars were identical in construction to the 4 cylinder cars and when plugged into a 4 cylinder cluster would provide the desired result.

Unfortunately, these coding plugs are out of production and are very difficult to source. The chip itself consists of one 8 pin IC chip. I've tried searching the model number printed on the top but it returns no results. The chip can be seen below:

My goal is to clone the chip by having a board printed and finding an appropriate IC chip to build the circuit upon. I am looking for advice on how I can identify this IC chip and if someone can identify it whether they can point me in the direction of an off the shelf solution.

Thanks, appreciate it

enter image description here

enter image description here

^^ Here are two images, however, these images show the 4cyl chip and not the 6cyl.

Yeah, I know there's thousands upon thousands of IC's. I was just hoping that someone had come across a similar situation. I've worked on black box circuits in the past and have been able to identify various filters from generating bode plots of the circuits at different frequencies but I'm not sure how to go about this for an IC chip. I was going to start by probing the connections on my car to figure out the inputs and outputs of the chip as well as constant power and ground. I could also look up the original wiring diagrams from BMW in some hope can figure out what each pin does by tracing back its connection. Any other advice on how to go about identifying this IC would be greatly appreciated.

UPDATE

So I managed to get in contact with the seller of the clone chip and he was kind enough to point me in the right direction, really awesome guy. Here's what he said:

The 8 pin IC I used is a microcontroller that acts as a coder - a device that uses a data set for scaling instrument cluster gauges. It is not an analogue signal converter.

Does anyone have any experience with coders for use with analogue guages?

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    \$\begingroup\$ You don't happen to know what the job of that IC that is? Basically, that could be anything, from a simple counter, to some memory, to a complete processor with RAM – there's not a few 8-pin ICs, there's literally tens of thousands. \$\endgroup\$
    – Marcus Müller
    Commented Jul 20, 2017 at 23:05
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    \$\begingroup\$ Big project! Good luck with it. I would suggest editing your question to include the chip markings, and all markings from the pcb - the images are a little hard to read. \$\endgroup\$
    – Blair Fonville
    Commented Jul 20, 2017 at 23:07
  • \$\begingroup\$ A search for "HML 087" turns up many people in the same predicament as you, and it doesn't appear to be solved in the many forum threads, so unlikely it will be solved here. "9022" appears to be the date code, FWIW. It might be a serial PROM and so you could try and pin it out by probing it while it's in circuit... \$\endgroup\$
    – uint128_t
    Commented Jul 21, 2017 at 0:13
  • \$\begingroup\$ The only thing i've come across is a guy in Lithuania who sells clone chips on ebay. I've got one of these chips and it works but he's taken due care scratching off the model number of the IC he used to create the coding plug. I don't think he's likely to tell me what IC he used as it would obviously affect his ebay business etc. But i'm confident to say he probably used an off the shelf chip. It's unlikely he had his own IC's manufactured right? I run a local enthusiast group and I'm hoping to help out some of the members with coding plugs. \$\endgroup\$
    – user156571
    Commented Jul 21, 2017 at 0:57

4 Answers 4

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From what I have found, which is not much, there seems to be some BMW-Refurbishers-Community consensus that HML 087 is an 8-pin EEPROM. I think probably a custom fabrication from Hughes - back when there existed such a manufacturing.

While identification from this schematic isn't very likely, it can help you to at least rule out possibilities:

bmw panel

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  • \$\begingroup\$ Thanks so much! I've spent ages trying to find this schematic. Definitely puts me a step closer \$\endgroup\$
    – user156571
    Commented Jul 23, 2017 at 1:19
  • \$\begingroup\$ @user156571 No problem. I only posted this section to make it more readable. If you want to reply with your email address, I'll send you the full schematic. \$\endgroup\$
    – Blair Fonville
    Commented Jul 23, 2017 at 3:06
  • \$\begingroup\$ thank you, that would be very helpful. My email is [email protected] \$\endgroup\$
    – user156571
    Commented Jul 25, 2017 at 2:40
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Maybe you should think about emulating the part instead of finding a exact replacement. If it's just a memory chip of some sort and you have both parts to compare, then maybe you can simply drop a logic analyzer on it, figure out what the protocol is, and program a small microcontroller to emulate it.

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Could be a clone of http://www.alldatasheet.com/datasheet-pdf/pdf/177121/TI/TL087.html. If it is an op-amp (probably is, considering you're talking about some sort of amplification), you could try it out. (I'm assuming your tacho is for indication purposes only)

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  • \$\begingroup\$ I thought so as well, when I was doing a little digging. But it cannot be. A schematic I found shows that it cannot be pin compatible with TL087. I'll post an answer with the schematic in case it helps the OP in his hunt. \$\endgroup\$
    – Blair Fonville
    Commented Jul 22, 2017 at 16:54
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The shown pictures show the BMW E30 Coder Stick. By changing the engine from 4-cyl to 6-Cyl, it's sufficient to replace the coder stick to a version for BMW 320i (part # 62111381635) or 325i (part # 62111381683). Both are still available at BMW.

The IC HML-087 is a serial 8-Bit EEPROM which are very very difficulty to re-program.

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  • \$\begingroup\$ Both named 320i & 325i Coder Sticks are still available in the German Spare part lists. Costs about € 50,-- each. If not available in your country, I'm able to re-program those BMW Instrument Cluster Coder Sticks (but not the board computer sticks). \$\endgroup\$
    – Abbakus
    Commented Nov 16, 2017 at 20:31

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