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LM2917N information requested

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vielle568

Member
Hello Out There,

I’m trying to connect the output from a LM2917N speed switch IC to control a MAX4514 analog switch. The analog switch is a CMOS device but what is the LM2917N? I can’t seem to find any info. If it’s not CMOS how do I interface the two chips? Any help gladly accepted. Thanks.

Vielle568

P.S. There are two versions of the LM2917N; 8 pin and 14 pin. I heard that the 8 pin chip will only accept an AC input whereas the 14 pin version will also accept pulsed DC. Can someone confirm this if it’s true? Thanks.
 

tcmtech

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Most Helpful Member

vielle568

Member
Thanks tcmtech,

But I have read the datasheet and I still can't figure out if the LM2917N is CMOS, TTL or whatever; it doesn't mention this in the specs. It also doesn't talk much about the differences between the 8 and 14 pin versions of the two chips. I've put together a circuit using the 8 pin version and the response does not track with accuracy. Perhaps this could be because the input comes straight off a 7555 giving pulses and not an AC signal. If the 14 pin chip does accept pulsed DC then perhaps I can change chips and solve the problem.

I'd like to understand the chip's format for interfacing purposes. Input comes from a 7555 timer (CMOS) and the output controls a MAX4514 analog switch (also CMOS). If the LM2917N isn't in the same family then there could be some connection problems.
 
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atferrari

Well-Known Member
Most Helpful Member
Your intention is not clear to me

Il y a quelque chosse, pas trés clair...

I cannot understand what you want to do.

The output from the 2917, is it going to be used to control the MAX switch or is it going to be fed to into the input pin ("NO")?

Please post an schematic showing:

a) what signal is being fed to the switch (NO pin)

b) what is the control signal to switch it ON/OFF (IN pin).

What a bad election of names for those pins...!
 

audioguru

Well-Known Member
Most Helpful Member
The LM2907/LM2917 is not Cmos but it can drive Cmos or TTL if its supply voltage for its pullup resistor is suitable.
The datasheet has these notes:
 

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vielle568

Member
OK, thanks audioguru, I think you have answered most of my questions. I admit that I didn't see these notes when reading the datasheet.

My circuit uses a 7555 chip as a monostable pulse generator that is triggered by a light sensor monitoring the speed of a perforated rotating wheel. The timer is used to clean up the signal and provide a clean square wave output. The signal passes to the LM2917N speed switch that is set up to give a high output on pin 5 when the input frequency passes the reference level. The output signal from pin 5 then goes on to trigger the analog switch and the LED.

It works, but the response time seems slow and inaccurate. It could be because I am using the 8 pin chip and should be using the 14 pin version. I'm not sure. If there are any other faults in the schematic please let me know. Thanks!
 

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audioguru

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I saw some missing resistors.
Try it like this:
 

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vielle568

Member
Thanks Again AudioGuru,

I knew I'd left something out. That's the trouble with being an ME and not an EE! Could I ask you to give me some ballpark figure for the resistor values? Thanks.

Incidently, if I pass an audio signal through the analog switch, do I need to have the chip wired to a +/- 5v supply or can a single +5v supply and ground be used?

Vielle568
 
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audioguru

Well-Known Member
Most Helpful Member
Your Cmos switch has a 0V to +5V supply so its signal must be biased at half the supply voltage at +2.5VDC.
 
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