[Diy_efi] Looking for some help on a speed sensor project

[Brian Dessent]

Perry Harrington wrote:

> Go to www.national.com and get the datasheets on the LM2907 and LM339.
> 
> The 2907 is a freq to voltage convertor and the 339 is a quad comparator.
> 
> Setup the 2907 for your frequency range and use a couple of the 339's
> comparators to make a window comparator.  Add a drive transistor and you
> got a speed switch.
> 
> I believe both circuit applications are even in the app notes section.

No need for the external parts.  The 2907 has a built in
opamp/comparator and NPN switching transistor (up to 50mA load) for this
very purpose.  p7 of the datasheet.

Brian

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