LM2917 to control a relay at threshold frequency

Discussion in 'The Projects Forum' started by Hpfiend, Feb 8, 2013.

  1. Hpfiend

    Thread Starter New Member

    Jan 11, 2013

    I am very new to integrated circuits! I am trying to understand the data sheet but most of it is beyond my comprehension... could anyone lend some help?

    I am looking at the datasheet for the LM2907/LM2917 frequency to voltage converters specifically figure 7 the speed switch.

    My questions are as follows:

    1) Can I control a relay as the load? I am assuming I need a LM2917 and apply additional current to the other side of the relay but I did not see anything in the circuit specifying anything other than the note above regarding zener regulated options. It says 6-24Vcc I am assuming that is generated voltage from the variable frequency or do I need to provide that somewhere?

    2) Can I use a 10K linear potentiometer to adjust R and just use say two 1uF capacitors? I will use the two 5K resistors shown in diagram.

    3) How do I induce "hysteresis" so that my circuit will not switch off and on quickly near threshold?

    Thank you for your help!
    Last edited: Feb 8, 2013
  2. Hpfiend

    Thread Starter New Member

    Jan 11, 2013
    I am a complete newbie! After lots of research I have purchased lots of parts and still can't get it to work!

    Using the schematic on page 9 of the pdf here
    figure 7 "Speed Switch" I have assembled a solderless breadboard.

    I used an LM2917N-8 and connected it as follows:

    OK first of all- I am assuming positioning the little half circle notch to the left with the text reading right side up from left to right is how you orient it? The bottom left most pin I call 1. and the bottom right most pin is 4

    pin 1 to frequency pulse positive
    pin 2 a 10uF capacitor and then to ground
    pin 3 a jumper to one side of 5.1K resistor (reads 4.97 on MM) then other leg jumper to ground
    pin 3 a 1uF capacitor in row of jumper and then other leg to ground
    pin 4 jumper to ground
    pin 5 ground side (outside) of 12 volt light bulb positive side of light bulb (center) is to the positive row.
    pin 6 one leg of 5.1K resistor and other leg to pin 7
    pin 6 jumper in same row and then to positive source (Vcc)
    pin 7 one leg of first 5.1K resistor (from pin 6) and then first leg of second 5.1 K resistor, the other leg goes to pin 8
    pin 8 final leg of pin 7 resistor and then a jumper in same row to ground
    I then have a 9 volt battery hooked up to the positive and ground rows
    Finally I have a jumper from the top row ground to the bottom row ground and then a ground jumper to ground of the frequency source

    Using 1/ (2RC) the threshold frequency to turn the bulb on should be 10 Hz.

    I tried a 10k linear potentiometer at R instead of the 5.1K resistor and set it to 5 with my multimeter and it did not work either

    I generated a known frequency using my arduino uno I just bought with a simple on pulse of 100 ms and then off for 100 ms in endless loop which if I did that math right should be 10 Hz. I checked it was pulsing with an LED. My arduino board is powered currently by USB so it should be 5 volts but I don't think it is bleeding through somehow... I wrote a program to make it pulse twice as fast at 50 ms on 50 ms off and it still didn't work. Oh yeah I am putting the positive frequency pulse jumper in the pulse pin and the ground jumper to ground on the arduino

    9 volt battery reads at 7.88 volts right now. This multimeter doesn't read capacitance, but my dad has one that does... light bulb works when connected directly.

    Should I be using the 2907 instead I bought one of those too as I couldn't figure out what the zener diode had to do with it and where it was...

    Please help!
    Last edited: Feb 20, 2013