Can''t get op-amp (LM358) to work.
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Posts: 46,084
At 03:51 AM 2/1/03 +0000, sunblock_98 <subhrajitb@h...> wrote:
>The LM358 has it's input tied to a phototransistor whose voltage is
>switching between 4.77 and 4.13 V (measured using multimeter). The
>reference voltage is around 4.52 V. The output of the op-amp remains
>unchanged at around 3.7 V. I tried both the op-amps in the LM358.
I am assuming that you are powering the LM358 from the 5V supply. If so,
the input common mode range is 0V through (Vcc-1.5) or about 3.5V.
Just for giggle and laughs, disconnect the output of the LM358 from the
stamp (so that you don't damage anything) and power the LM358 from the
unregulated input on the Stamp (9V). You should now see everything working
as you expect.
In general, the LM358 is a poor choice in a 5V only system because of the
limited input and output range. I'll post the results of a single supply
op-amp search I did a week or so ago - the parameter I was looking for in
this search was a low input-offset part but all the rail to rail parts I
list (shown as RR) are probably suitable for your use.
Note that I do use the LM358 (and LM324) in many of my products but I run
the chips from the unregulated supply (+17V in most of my stuff). I then
ensure that I don't over-drive the inputs of any 5V chips.
<list starts>
Low cost single supply dual op-amps
Input & output go down to GND
Prices in Can $ @ 100 pieces Jan 2003 Arrow Electronics
AD = Analog Devices, LT = Linear Technology, TI = Texas Instruments,
NS = National Semiconductor, MCP = Microchip
Part Manufct VIOS V0hi Supply Price
# (mV) (min) range C$ @100
AD8552 AD 0.003 R-R 2.7 - 5 4.39
LT1013 TI 0.3 Vcc-1 5..40 0.88
LT1013D TI 0.8 Vcc-1 5..40 0.89
TLE2022 TI 0.15 Vcc-1 4..40 1.05
TLC2272 TI 0.95 R-R 4.4 - 16 0.99
LMC6082 NS 0.35 R-R 4.5 - 15.5 2.15
LMC6462 NS 0.50 R-R 3 - 15.5 2.13
LMC6482 NS 0.75 R-R 3 - 15.5 0.88
LMV712 NS 0.40 R-R 2.7 - 5 1.22 @ 1000 MOQ
MCP607 MCP 0.25 R-R 2.5 - 5.5 1.17
MCP617 MCP 0.15 R-R 2.3 - 5.5 1.26
MCP6022 MCP 0.50 R-R 2.5 - 5.5 1.59
Hope this helps!
--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 18 years of Engineering Innovation (1984 - 2002)
.-. .-. .-. .-. .-. .-. .-. .-. .-. .-
`-' `-' `-' `-' `-' `-' `-' `-' `-'
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.
>The LM358 has it's input tied to a phototransistor whose voltage is
>switching between 4.77 and 4.13 V (measured using multimeter). The
>reference voltage is around 4.52 V. The output of the op-amp remains
>unchanged at around 3.7 V. I tried both the op-amps in the LM358.
I am assuming that you are powering the LM358 from the 5V supply. If so,
the input common mode range is 0V through (Vcc-1.5) or about 3.5V.
Just for giggle and laughs, disconnect the output of the LM358 from the
stamp (so that you don't damage anything) and power the LM358 from the
unregulated input on the Stamp (9V). You should now see everything working
as you expect.
In general, the LM358 is a poor choice in a 5V only system because of the
limited input and output range. I'll post the results of a single supply
op-amp search I did a week or so ago - the parameter I was looking for in
this search was a low input-offset part but all the rail to rail parts I
list (shown as RR) are probably suitable for your use.
Note that I do use the LM358 (and LM324) in many of my products but I run
the chips from the unregulated supply (+17V in most of my stuff). I then
ensure that I don't over-drive the inputs of any 5V chips.
<list starts>
Low cost single supply dual op-amps
Input & output go down to GND
Prices in Can $ @ 100 pieces Jan 2003 Arrow Electronics
AD = Analog Devices, LT = Linear Technology, TI = Texas Instruments,
NS = National Semiconductor, MCP = Microchip
Part Manufct VIOS V0hi Supply Price
# (mV) (min) range C$ @100
AD8552 AD 0.003 R-R 2.7 - 5 4.39
LT1013 TI 0.3 Vcc-1 5..40 0.88
LT1013D TI 0.8 Vcc-1 5..40 0.89
TLE2022 TI 0.15 Vcc-1 4..40 1.05
TLC2272 TI 0.95 R-R 4.4 - 16 0.99
LMC6082 NS 0.35 R-R 4.5 - 15.5 2.15
LMC6462 NS 0.50 R-R 3 - 15.5 2.13
LMC6482 NS 0.75 R-R 3 - 15.5 0.88
LMV712 NS 0.40 R-R 2.7 - 5 1.22 @ 1000 MOQ
MCP607 MCP 0.25 R-R 2.5 - 5.5 1.17
MCP617 MCP 0.15 R-R 2.3 - 5.5 1.26
MCP6022 MCP 0.50 R-R 2.5 - 5.5 1.59
Hope this helps!
--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 18 years of Engineering Innovation (1984 - 2002)
.-. .-. .-. .-. .-. .-. .-. .-. .-. .-
`-' `-' `-' `-' `-' `-' `-' `-' `-'
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.