Op Amp to BS2 Blues
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I constructed the amplifier circuit shown in N&V column #57 to
connect to an ADC as described, except for changing the gain resistor
to 202 ohms (to provide a gain of 100). After trouble shooting the
circuit a number of times, I still can't get any amplification of the
sensor output. The OP amp output measures about 0.3 volts and does
not change with changing input mV. I measured the sensor and can
read changing mV with increasing presssure so I feel like the sensor
works correctly. Is the circuit correct as shown? Does anyone have
any ideas on checking the op amp ICs or how I can split the circuit
and troubleshoot each IC? Any help would greatly appreciated.
Walt Beckwith
connect to an ADC as described, except for changing the gain resistor
to 202 ohms (to provide a gain of 100). After trouble shooting the
circuit a number of times, I still can't get any amplification of the
sensor output. The OP amp output measures about 0.3 volts and does
not change with changing input mV. I measured the sensor and can
read changing mV with increasing presssure so I feel like the sensor
works correctly. Is the circuit correct as shown? Does anyone have
any ideas on checking the op amp ICs or how I can split the circuit
and troubleshoot each IC? Any help would greatly appreciated.
Walt Beckwith
Comments
wrote:
> I constructed the amplifier circuit shown in N&V column #57 to
> connect to an ADC as described, except for changing the gain
resistor
> to 202 ohms (to provide a gain of 100). After trouble shooting the
> circuit a number of times, I still can't get any amplification of
the
> sensor output. The OP amp output measures about 0.3 volts and does
> not change with changing input mV. I measured the sensor and can
> read changing mV with increasing presssure so I feel like the
sensor
> works correctly. Is the circuit correct as shown? Does anyone
have
> any ideas on checking the op amp ICs or how I can split the
circuit
> and troubleshoot each IC? Any help would greatly appreciated.
> Walt Beckwith
Hi Walt,
Can you post a layout of your unit ?
Are you breadboarding it ? maybe a pic ?
Dave
the input drive voltage source ground at the same potential as the device
(op amp) ground. This is easy to overlook.
jim
http://www.geocities.com/jimforkin2003/
Original Message
From: Dave Mucha [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=27mInqKEgxNp48bS6GyT6iQ4uhSosDbSBHf52OBFK8jDDRFi6GW_g_xG8PXedkDF-avwJDQu97N3TA]davemucha@j...[/url
Sent: Thursday, March 25, 2004 10:01 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: Op Amp to BS2 Blues
--- In basicstamps@yahoogroups.com, "waltb27707" <wbeckwith@m...>
wrote:
> I constructed the amplifier circuit shown in N&V column #57 to
> connect to an ADC as described, except for changing the gain
resistor
> to 202 ohms (to provide a gain of 100). After trouble shooting the
> circuit a number of times, I still can't get any amplification of
the
> sensor output. The OP amp output measures about 0.3 volts and does
> not change with changing input mV. I measured the sensor and can
> read changing mV with increasing presssure so I feel like the
sensor
> works correctly. Is the circuit correct as shown? Does anyone
have
> any ideas on checking the op amp ICs or how I can split the
circuit
> and troubleshoot each IC? Any help would greatly appreciated.
> Walt Beckwith
Hi Walt,
Can you post a layout of your unit ?
Are you breadboarding it ? maybe a pic ?
Dave
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202 ohms seems a little low to provide a gain of 100X. Try a pot of 100k and
see what happens. What is the value of the input resistor? I *think* that
the gain resistor / input resistor = gain.
Jonathan
www.madlabs.info
Original Message
From: "waltb27707" <wbeckwith@m...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, March 25, 2004 6:58 PM
Subject: [noparse][[/noparse]basicstamps] Op Amp to BS2 Blues
> I constructed the amplifier circuit shown in N&V column #57 to
> connect to an ADC as described, except for changing the gain resistor
> to 202 ohms (to provide a gain of 100). After trouble shooting the
> circuit a number of times, I still can't get any amplification of the
> sensor output. The OP amp output measures about 0.3 volts and does
> not change with changing input mV. I measured the sensor and can
> read changing mV with increasing presssure so I feel like the sensor
> works correctly. Is the circuit correct as shown? Does anyone have
> any ideas on checking the op amp ICs or how I can split the circuit
> and troubleshoot each IC? Any help would greatly appreciated.
> Walt Beckwith
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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Body of the message will be ignored.
>
> Yahoo! Groups Links
>
>
>
>
>
>
Thank you for your replies. I hard wired the circuit on ONE PAS
board and put the two OPA 2340 ICs in sockets. I don't have a
photo. The circuit is at:
http://www.parallax.com/dl/docs/cols/nv/vol2/col/nv57.pdf Figure
57.2
The gain is calculated by: Vout=(Vhigh-Vlow) (1+2R1/Rgain) R1 is 10K
ohms. The circuit was wired up with 0.22uF bypass caps wired between
pins 4 (-) and 8 (+) on each OPA 2340. I am powering the circuit with
12 volts (8 AA batteries) 12 volts energizes the sensor input
leads. I have a 7805 regulator that drops the voltage to 4.89 volts
which powers the op amps. There is a common ground between 12 volt
and 4.89 volt side. The V low sensor output is not grounded. I'm
not sure how to check ground potentials. I get 4.89 volts from any
regulated positive to any grounded pin or wire with a Radio Shack
DMM.
According to the Spec sheet the OPA2340 can be run from a single
supply of 2.5 to 5.5 volts. Which is what I did. There is nothing
about running from a split supply. I'm beginning to think another amp
might be a better choice.
Thanks for the ideas Guys. I will keep checking.
>>>>>>>>>>>>>
I constructed the amplifier circuit shown in N&V column #57 to
> connect to an ADC as described, except for changing the gain
resistor
> to 202 ohms (to provide a gain of 100). After trouble shooting the
> circuit a number of times, I still can't get any amplification of
the
> sensor output. The OP amp output measures about 0.3 volts and does
> not change with changing input mV. I measured the sensor and can
> read changing mV with increasing presssure so I feel like the
sensor
> works correctly. Is the circuit correct as shown? Does anyone
have
> any ideas on checking the op amp ICs or how I can split the
circuit
> and troubleshoot each IC? Any help would greatly appreciated.
> Walt Beckwith
--- Walter Beckwith
--- wbeckwith@m...
--- EarthLink: The #1 provider of the Real Internet.
providing from the sensors to the op amps, add the gain for the difference
between the two, and I suspect you're out of range especially since the op
amp is running from 5 volts. You are dealing with a gain of about 50 so .1
volts on the input would put you at the rail on the output.
jim
http://www.geocities.com/jimforkin2003/
Original Message
From: waltb27707 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=W2480LznMIeZ9fUZ1K8aIuarJC6NLQB3neYYNs7dBOgckviQT6E7mredKeHRzeHpThORL73XxSDeLa2fM39xP-Pf]wbeckwith@m...[/url
Sent: Sunday, March 28, 2004 10:12 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Op Amp to BS2 Blues
Dave, Jim, and Jonathan,
Thank you for your replies. I hard wired the circuit on ONE PAS
board and put the two OPA 2340 ICs in sockets. I don't have a
photo. The circuit is at:
http://www.parallax.com/dl/docs/cols/nv/vol2/col/nv57.pdf Figure
57.2
The gain is calculated by: Vout=(Vhigh-Vlow) (1+2R1/Rgain) R1 is 10K
ohms. The circuit was wired up with 0.22uF bypass caps wired between
pins 4 (-) and 8 (+) on each OPA 2340. I am powering the circuit with
12 volts (8 AA batteries) 12 volts energizes the sensor input
leads. I have a 7805 regulator that drops the voltage to 4.89 volts
which powers the op amps. There is a common ground between 12 volt
and 4.89 volt side. The V low sensor output is not grounded. I'm
not sure how to check ground potentials. I get 4.89 volts from any
regulated positive to any grounded pin or wire with a Radio Shack
DMM.
According to the Spec sheet the OPA2340 can be run from a single
supply of 2.5 to 5.5 volts. Which is what I did. There is nothing
about running from a split supply. I'm beginning to think another amp
might be a better choice.
Thanks for the ideas Guys. I will keep checking.
>>>>>>>>>>>>>
I constructed the amplifier circuit shown in N&V column #57 to
> connect to an ADC as described, except for changing the gain
resistor
> to 202 ohms (to provide a gain of 100). After trouble shooting the
> circuit a number of times, I still can't get any amplification of
the
> sensor output. The OP amp output measures about 0.3 volts and does
> not change with changing input mV. I measured the sensor and can
> read changing mV with increasing presssure so I feel like the
sensor
> works correctly. Is the circuit correct as shown? Does anyone
have
> any ideas on checking the op amp ICs or how I can split the
circuit
> and troubleshoot each IC? Any help would greatly appreciated.
> Walt Beckwith
--- Walter Beckwith
--- wbeckwith@m...
--- EarthLink: The #1 provider of the Real Internet.
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