I bought a LM2907 and im trying to build a tachometer for a RC car.
I've looked at the schematics and I've tried to test the ic by
inputing a pulse of 1Khz , 250mVPP waveform in the input but i am not
getting anything in the output. Do you guys have any suggestions in
what i can do to try to test this IC correctly.

On 8/22/07 2:23 PM, in article
1187817800.732446.170140@i38g2000prf.googlegroups.com, "alfredr1@msn.com"
<alfredr1@msn.com> wrote:

> I bought a LM2907 and im trying to build a tachometer for a RC car.
> I've looked at the schematics and I've tried to test the ic by
> inputing a pulse of 1Khz , 250mVPP waveform in the input but i am not
> getting anything in the output. Do you guys have any suggestions in
> what i can do to try to test this IC correctly.
>

Post the schematic so it can be reviewed.

On Wed, 22 Aug 2007 14:23:20 -0700, alfredr1@msn.com wrote:

>I bought a LM2907 and im trying to build a tachometer for a RC car.
>I've looked at the schematics and I've tried to test the ic by
>inputing a pulse of 1Khz , 250mVPP waveform in the input but i am not
>getting anything in the output. Do you guys have any suggestions in
>what i can do to try to test this IC correctly.

---
http://cache.national.com/ds/LM/LM2907.pdf


--
JF

On Aug 23, 12:34 pm, John Fields <jfie...@austininstruments.com>
wrote:
> On Wed, 22 Aug 2007 14:23:20 -0700, alfre...@msn.com wrote:
> >I bought a LM2907 and im trying to build a tachometer for a RC car.
> >I've looked at the schematics and I've tried to test the ic by
> >inputing a pulse of 1Khz , 250mVPP waveform in the input but i am not
> >getting anything in the output. Do you guys have any suggestions in
> >what i can do to try to test this IC correctly.
>
> ---http://cache.national.com/ds/LM/LM2907.pdf
>
> --
> JF

from what i can tell, you got one input to the opamp which is the
reference speed you want to be at. you got another input to the opamp
which is its present speed. And you got the opamp's output
controlling the flow of a bigger current through a bipolar
transistor.

but since there is no negative feedback shown, the opamp will be
driven to the rails and the transistor will only stop conducting when
the reference speed has been equalled or slightly exceeded.

am i right here folks?

PS : I'm just a newbie so please note my ramblings with caution.