Re: Opamp and circuit help please.
From: Jamie (jamie_5_not_valid_after_5_Please_at_charter.net)
Date: 08/08/04
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Date: Sun, 08 Aug 2004 12:48:29 -0700
its simple.
look for a single chip DC-DC inverter.
design your circuit to operate like at
5 volts.
they have Converters that will maintain
5 volts even when the input voltages gets
down as low as 1 volt.
if you don't want to do that then use a
high efficiency type.
below is a link to a reg that should handle the operation of
at least your reciver and comparator.
http://www.micrel.com/product-info/products/mic2954.shtml
Rubicon wrote:
> Hello,
>
> I have been trying to make a 40kHz ultrasonic transmitter and receiver
> without much success until the recent "Opamp problem" post and the
> subsequent replies. It answered many questions for me.
> My desire is to have the receiver battery powered and be reliable.
>
> I have put a schematic on the net at:
> http://www.geocities.com/talionis.geo/Temp/temp.html
>
> Unable to locate a suggested LM6132 low power opamp locally I am
> trying a LM833 in its place. With the LM833 (GBW of 10MHz min - 15MHz
> max, slew rate of 7V/uS) I set both halves of the opamp with a 1K and
> 33K for a gain of 33*33=1089.
> The square root of a desired 1000 stage gain = 31.6 so a standard
> value 33K negative feedback resistor was chosen for each stage. The
> GBP would then be 10*33*40000=13.2MHz which is within the upper and
> lower limits of the LM833. Correct so far?
>
> There is a LM393 comparator in place of an LM358 opamp as with a
> transistor based receiver circuit I built with a CA3140 opamp as a
> comparator (1.5m range) I found that a drop in battery voltage caused
> it to stop working. Re-adjusting the threshold trimmer fixed this but
> I don't want to have to keep doing that as the battery depletes.
>
> I've made the D1, D2 diodes schottky types, not quite the right ones I
> know. 1SS106 barrier diodes would be better but are unavailable.
>
> The yellow dots on the schematic are some things I'm not very sure
> about. What are the functions of R4, C2 and C14 and are their values
> correct?
> Do I need to add anything to have a long shielded cable to TX1?
>
> I have a basic 555 transmitter I made for the transistor based
> receiver circuit and using it on the above LM833 circuit it didn't
> work at all. Changing the opamps resistor values to Part-A 10k/1M and
> Part-B 10k/100K from a printed off rangefinder circuit it did but at
> only 2-3cm.
> I am not sure why the transmitter worked on the second setup and not
> the first. I read where it'd be better to stay away from large value
> resistors to decrease noise with such high gain. It's not the best
> transmitter but it must have been roughly tuned to 40kHz to work at
> all. I do not have a scope to measure it but I have seen a frequency
> meter kitset that I think might just do to tune it or its replacement.
>
> The transmitter on the schematic I haven't yet built.
>
> Any help always appreciated.
>
> Andrew.
- Next message: Jamie: "Re: Negative Voltage"
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