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LM1815: At Mode 2 (Pin 5 connected to +V) is the adaptive threshold active or is the armed trigger level fixed to 200mV?

Bernd Scheifele
Prodigy 10 points
Part Number: LM1815

Tool/software:

My understanding is, that in Mode 2 the initial threshold is set to 200mV and if  the sensor voltage signal is higher than these threshold, the adaptive theshold is set to 80% of the peak value.

Please acknowledge or correct me.

  • 0
    TI__Mastermind 41235 points

    Hi Bernd,

    Mode 2 has a fixed threshold. This is what distinguishes the different modes. Only Mode 1 has the adaptive functionality.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 10 points

    Hello,
    is it possible to change the mode during the LM1815 is evaluating a spped signal?
    Application is to evaluate the engine speed signal of a diesel engine for commercial vehicles (heavy duty engines).
    The idea behind is, to start with Mode 2 (threshold at 200mV) cranking with electric starter.
    When the speedsignal is evaluated and the engine is running in fired mode with higher rpm, the amplitude of the speedsignal is higher too. Then we can switcht over to Mode1 with adaptive threshold,  to make the system mor robust.

  • 0 in reply to Bernd Scheifele
    Prodigy 10 points

    Is it possible to switch over the evaluation mode without switching OFF/ON of the supply voltage?

  • 0 in reply to Bernd Scheifele
    TI__Mastermind 41235 points

    It's an analog circuit, so it will change it's operation. However, there is a concern that there could be unwanted behavior or glitching during the switch. Additionally, Mode 1 relies on an open circuit. Depending on how you drive the pin to make the switch, you may struggle to get LM1815 to reliably detect the open state with a circuit attached to it. 

    I would also recommend asking for help with RPM detection in the amplifier forum. There may be newer solutions for this application that we don't have visibility to in the sensor forum.

    thanks,

    ren