05-24-2021, 03:45 AM
Hi there!
It's been a long time!
I finally got around to trying the relay and transistor circuit posted on the Megasquirt forums. (this one :https://www.msextra.com/forums/viewtopic.php?f=131&t=40365).
I can confirm that it works quite well. Probing the output, I got about 45v RMS on my Chinese scope (it says that the max input voltage is 40v, but I read somewhere on the internet that it's an easy fix even if it breaks).
Tach works! The relay is being switched so fast, that it doesn't have enough time to spring back, so it doesn't even click when the engine is running.
Meanwhile, the little Immo emulator that I had used let out the magic smoke. For the past year I have been learning and doing flash tunes on cars, and have had to disable a few immos as well. I have accumulated quite a large library of different immo software by now, so I decided to try one of the programs, which seemed to support these HITACHI ECUs. The program only changed a single byte from the EEPROM dump and the car fired right up, but upon trying to restart it, the MIL started blinking again and the immo was once again locked. Reading the EEPROM again, turns out, that the CPU overwrites said byte every restart, or every other restart. There is a variation of the 93c46 EEPROM that can be write locked by the programmer, but I had to order them from china, so I got to thinking. I ended up using an Arduino NANO, as an EEPROM programmer and just glued it to the inside of the ECU. One pin detects when the ignition goes from ON to OFF (via a voltage divider, since the arduino can't take 12v) and just starts hammering the EEPROM with write commands to the proper address. I decided to do it with the ignition off, because I wanted to make sure that the CPU wasn't accessing the EEPROM while the Arduino was also trying to access it. In the next post, I will post a short explanation on how I did it, so if anyone ever needs to do it will hopefully find it helpful.
It's been a long time!
I finally got around to trying the relay and transistor circuit posted on the Megasquirt forums. (this one :https://www.msextra.com/forums/viewtopic.php?f=131&t=40365).
I can confirm that it works quite well. Probing the output, I got about 45v RMS on my Chinese scope (it says that the max input voltage is 40v, but I read somewhere on the internet that it's an easy fix even if it breaks).
Tach works! The relay is being switched so fast, that it doesn't have enough time to spring back, so it doesn't even click when the engine is running.
Meanwhile, the little Immo emulator that I had used let out the magic smoke. For the past year I have been learning and doing flash tunes on cars, and have had to disable a few immos as well. I have accumulated quite a large library of different immo software by now, so I decided to try one of the programs, which seemed to support these HITACHI ECUs. The program only changed a single byte from the EEPROM dump and the car fired right up, but upon trying to restart it, the MIL started blinking again and the immo was once again locked. Reading the EEPROM again, turns out, that the CPU overwrites said byte every restart, or every other restart. There is a variation of the 93c46 EEPROM that can be write locked by the programmer, but I had to order them from china, so I got to thinking. I ended up using an Arduino NANO, as an EEPROM programmer and just glued it to the inside of the ECU. One pin detects when the ignition goes from ON to OFF (via a voltage divider, since the arduino can't take 12v) and just starts hammering the EEPROM with write commands to the proper address. I decided to do it with the ignition off, because I wanted to make sure that the CPU wasn't accessing the EEPROM while the Arduino was also trying to access it. In the next post, I will post a short explanation on how I did it, so if anyone ever needs to do it will hopefully find it helpful.