LM1815 help
eagletalontim
Posts: 1,399
Hello all again. I am having some difficulty with reading my friends vehicle's output shaft pulse generator using the LM1815 as recommended in a previous thread quite awhile ago. The circuit board I made is designed to like the diagram on this link : http://www.matt_phoenix.talktalk.net/Diary-December2009.html
I have tried both ways, but cannot get an accurate reading at low speed with the first diagram and can only get an accurate reading under 18mph with the second. Any help is appreciated!
EDIT * I did not remove pin 8 from the +5V as shown in the second diagram. Not sure if that helps or not. Pin 8 is V+
I have tried both ways, but cannot get an accurate reading at low speed with the first diagram and can only get an accurate reading under 18mph with the second. Any help is appreciated!
EDIT * I did not remove pin 8 from the +5V as shown in the second diagram. Not sure if that helps or not. Pin 8 is V+
Comments
I would suggest starting with circuit 1, but remove the 300 ohm resistor from the circuit. You may also need to reduce the size of the capacitor on pin 14. If the output pulse is too wide it will limit how high a speed you can measure. If you have a scope perhaps you can measure and post the pulse width, frequency, and p-p voltage at various speeds.
Here is some information on the pin functions of the LM1815 from the data sheet.
Pin 3 is the input signal from the variable reluctance sensor to be processed. Since I have no information on the sensor all I can say about it is the resistors and capacitor values look reasonable.
Pin 5 is the mode select pin. Left floating selects adaptive mode.
Connect to +5V for a 200mV threshold so the input signal must be at least 400mVp-p to produce an output pulse.
Connect to ground for a 0V threshold so the input signal must be at least 25mVp-p to produce an output pulse
Pin 7 is the peak detector capacitor. It is used to set the threshold in adaptive mode
Pin 8 is +5V in to the chip so it is required. So is the GND on pin 2.
Pin 11 selects which signal is gated out on pin 10. A high (+5V) selects the signal input on pin 9. Low selects the internal signal from the on chip one shot. Since the output on pin 10 is not used it does not matter if it is high or low, as long as it is not left floating.
Pin 12 is an open collector transistor controlled by the internal one shot so the 4.7K resistor to +5V is required.
Pin 14 is for the RC circuit (39K/0.01uF) that sets the time duration of the output pulse on pin 12 in this circuit.