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frosting

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  1. Hi Daniel, Thanks for doing this and for all the documentation you did in your wiki. In your memory diagram you show 512 byte Information memory, but it is from addresses 0x01000 to 0x010FF, only 256 bytes. It has been a while since I looked at information memory in the '2553 but I remember it being 4 * 64 bytes. Best regards, Bob
  2. I'm not trying to start anything here, but if you look inside a car's ECU you will not find a single optoisolator.
  3. It's not bad, either positive or negative requires pretty much the same treatment. I have designed many products used in autos and trucks. A resistor, a capacitor, and a Zener diode is ample protection for an input pin. If you are using the internal pullup or pulldown in the MSP430 then it might influence the choice of resistor value, use a higher value if you are sensing a 12V signal(4.7K or 10K is fine). But the basic three parts are all you need. Use a white or blue LED if you don't have a 3.3V Zener. Or two reds in series. Regards, Bob
  4. Hi Andreas, No product designed for use in a car would do this. But you can probably get away with it. Basically there are two issues. One is obvious, what happens if the wire contacts 12V? At best, the MSP430 would lose that pin, permanently. The second issue is that a long wire that leaves your circuit is an antenna. You can get false inputs, and in a bad case, latchup. It is also a minor source of EMI leaving your circuit. At the very least, please put a low value (470 ohms is a good choice) in series with the MSP430 input pin before it leaves the enclosure. For full protection, also add a low value (10nF) capacitor from MSP430 input pin to ground. Parallel the capacitor with a small zener diode, 3 to 3.6 V. Cheers, Bob
  5. Isn't the PCF8574 an I2C to 8-bit interface? The HD44780 display has a few control lines in addition to data, so you are probably running in 4-bit mode, with 4 of the pins for data plus RS, RW and EN. Each character will take two complete transactions. And the EN pin is how you clock in each byte. If you have the EN pin connected to your PCF8574 you will need four I2C instructions to print one character. If you clock the display separately from the PCF8574 then it only takes two I2C writes, but they need to be interspersed with clocking of the display's EN pin.
  6. No need to use a sine wave. Generate square waves with the MSP430. One end of your sensor goes to the pin with the square wave, the other to the midpoint of a voltage divider of the MSP430 power supply. Tie the input of an A/D channel there, take measurements at both polarities of the square wave and subtract one from the other for the net voltage. Essentially a bridge circuit, your unknown is working against the impedance of the voltage divider. If your resistors are 2K then the impedance of the divider is 1K. Choose the resistors to scale the sensor gel. If the impedance is too low you will load the MSP430 output, too high and the A/D converter will have offset errors (and S/H errors if you use more than one channel). All of those problems can be worked around with more parts, but you have the basis for a full system of one channel with only two resistors, two channels with only four resistors. Make sure you never stop the square wave unless you turn the pin into an input! Else your sensor will have electrolytic damage. Hope this helps.
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