Maxim 9924 Help needed

Post Reply
Posts: 1
Joined: Wed Feb 11, 2015 6:44 pm

Maxim 9924 Help needed

Post by ginger444w » Wed Feb 11, 2015 7:43 pm

Thank you all for reading my post as it is my first on this forum. I have purchased the max9924 vr sensor and proto_advantage adapter board to build a circuit to translate the signal from a HEI distributor into a square wave to be fed into a microcontroller. I am using "a2" mode and have built the circuit as it appears in the datasheet. I power the circuit with a 9v battery which is fed into a 7805 voltage regulator with the necessary filtering caps that gives me 4.97 volts at the vcc pin on the max9924. My current is running in the tolerance as per the datasheet of 2.6-5ma. I have also removed the voltage regulator and 9v battery and powered this circuit with a regulated dc power supply at the nominal 5.0 volts and used a resistor to give me 2.6ma typ. per the datasheet. I am using the 10k resistors and 1nf cap on the in+/ in- pins 1 and 2. Pin three is left open(floating) with pin 4 Bias tied to ground. Pin 5 in obviously tied to ground as is pin 6. Pin 7 has a 10k pull up resistor( to be removed when used with the microcontroller as it has internal pull ups on the i/o pins) as I was using it to test the square wave with my oscilloscope. Pin 8 is open(gloating) Pin 9 is tied to ground and pin 10 is the vcc as mentioned above. Here in is where I run into problems. I know my soldering is ok as I have yrs of soldering experience and have checked the pins and adjacent pins with my meter and all are fine (no shorts as I also checked it under a microscope). When I hook up my oscilloscope to pin 7 (cout) (and also ground the scope probe) and monitor the square wave it looks really good but I am only seeing 0-.5(500mv) or .6 (600mv)volts. I was thinking I would be seeing 0-5volts or something close to that amount. I also know it is incorrect because my microcontroller needs to see at least .7 volts on the input pin. I have read, read and read the data sheet, torn the circuit apart and rebuilt it several times but to have the same results of only .5-.6volts. In googling the chip I found scope shots that clearly show the correct voltage.
If anyone has any feedback or help or has seen this before I would appreciate the help.


Posts: 3655
Joined: Sat Oct 03, 2009 12:24 pm
Location: Quebec, Canada

Re: Maxim 9924 Help needed

Post by jbelanger » Wed Feb 11, 2015 8:15 pm

If you followed the mode A2 circuit as per the datasheet, then it should work. Have you checked that the input signal is ok? Is everything grounded to the same ground? Have you tried using a 0-5V (or 0-12V) square wave output only connected to VR+ (or VR-) with the other input left floating?

As I said, if you followed the datasheet it should work. That is a very simple circuit and it simply works. And I don't want to be rude but I should add that this forum is for support of my products not for generic circuit building that use the same chips I do.


Post Reply