voltage ramp
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hi
im building a machine that will be controlled by at least 4 bs2's.
ive got everything worked out but for one thing.
the workheads are shifted along tracks to set positions using hydraulic
cylinders. the problem is these workheads are HEAVY
so i have proportional valves running the cylinders.
what i need is to supply the valves with a ramping voltage from
0v - 10v to start them running and an opposite ramp at the end of their
travel (or just prior to the end actually).
ive been playing with r/c circuits with partial success but would like
the ramp to be more linear. any ideas out there?
the ramp up/down time should be from 0 to 1 second (adjustable).
any input would be greatly appreciated.
ian
im building a machine that will be controlled by at least 4 bs2's.
ive got everything worked out but for one thing.
the workheads are shifted along tracks to set positions using hydraulic
cylinders. the problem is these workheads are HEAVY
so i have proportional valves running the cylinders.
what i need is to supply the valves with a ramping voltage from
0v - 10v to start them running and an opposite ramp at the end of their
travel (or just prior to the end actually).
ive been playing with r/c circuits with partial success but would like
the ramp to be more linear. any ideas out there?
the ramp up/down time should be from 0 to 1 second (adjustable).
any input would be greatly appreciated.
ian
Comments
I will need a ramping voltage, and intend to have a Stamp count up, (and
down), and output the count to a serial D/A converter. The rate is
controllable with a pause statement.
Ray McArthur
Original Message
From: Ian Lawson <irlawson@i...>
To: <basicstamps@egroups.com>
Sent: Friday, April 07, 2000 11:43 PM
Subject: [noparse][[/noparse]basicstamps] voltage ramp
> hi
> im building a machine that will be controlled by at least 4 bs2's.
> ive got everything worked out but for one thing.
> the workheads are shifted along tracks to set positions using hydraulic
> cylinders. the problem is these workheads are HEAVY
> so i have proportional valves running the cylinders.
> what i need is to supply the valves with a ramping voltage from
> 0v - 10v to start them running and an opposite ramp at the end of their
> travel (or just prior to the end actually).
> ive been playing with r/c circuits with partial success but would like
> the ramp to be more linear. any ideas out there?
> the ramp up/down time should be from 0 to 1 second (adjustable).
> any input would be greatly appreciated.
> ian
>
>
>
>
>
>Ian:
>I will need a ramping voltage, and intend to have a Stamp count up, (and
>down), and output the count to a serial D/A converter. The rate is
>controllable with a pause statement.
>
>Ray McArthur
>
>
Original Message
>From: Ian Lawson <irlawson@i...>
>To: <basicstamps@egroups.com>
>Sent: Friday, April 07, 2000 11:43 PM
>Subject: [noparse][[/noparse]basicstamps] voltage ramp
>
>
>> hi
>> im building a machine that will be controlled by at least 4 bs2's.
>> ive got everything worked out but for one thing.
>> the workheads are shifted along tracks to set positions using hydraulic
>> cylinders. the problem is these workheads are HEAVY
>> so i have proportional valves running the cylinders.
>> what i need is to supply the valves with a ramping voltage from
>> 0v - 10v to start them running and an opposite ramp at the end of their
>> travel (or just prior to the end actually).
>> ive been playing with r/c circuits with partial success but would like
>> the ramp to be more linear. any ideas out there?
>> the ramp up/down time should be from 0 to 1 second (adjustable).
>> any input would be greatly appreciated.
>> ian
>
Gents:
I'm not quite sure I understand how these workheads operate, nor do I find my
expertise in analog electronics, but - does this help:
PWM pin, duty, cycles
Convert a digital value to analog output via pulse-width modulation.
• Pin is a variable/constant (0-15) that specifies the I/O pin to use.
This pin will be placed into output mode during pulse generation
then switched to input mode when the instruction finishes.
• Duty is a variable/constant (0-255) that specifies the analog output
level (0 to 5V).
• Cycles is a variable/constant (0-65535) specifying an approximate
number of milliseconds of PWM output.
That would give you a voltage of 0-5V over a variable time period (scaled
as may
be required). Going from 0-5V could be 0-10V if run through a x2 gain
op-amp -
and smoothing could be with a cap. (if required) - yes ? no ? Maybe I've
got the
wrong idea <shrug>.
Regards,
Bruce
>
>
>
>
>> what i need is to supply the valves with a ramping voltage from
>> 0v - 10v to start them running and an opposite ramp at the end of their
>> travel (or just prior to the end actually).
>> ive been playing with r/c circuits with partial success but would like
>> the ramp to be more linear. any ideas out there?
>> the ramp up/down time should be from 0 to 1 second (adjustable).
Bruce suggested:
> PWM pin, duty, cycles...
Just to expand a bit on Bruce's suggestion to use PWM: The command would
have to be enclosed in a loop in order to ramp up the voltage. The PWM must
be filtered with an RC circuit, feeding a buffer amplifier up to the
desired 10 volt level.
' enter with P0 low, off
cy=16 ' set the ramp-up rate
for dt=0 to 255 step 5 ' ramp up on P0
PWM 0,dt,cy ' gradually increase duty cycle
next
high 0 ' keep it high
One cycle takes 1.15 millisecond (the manual says "approximately" one
millisecond). For the record, the maximum value of cycles is 255 (The
manual says 65535, but that is just wrong.)
The above for-next loop has 52 steps, and takes 52*1.15=60 milliseconds
when the value of cy=1. Enter the loop with cy=16 and ramp up from 0 volts
to 5 volts in 0.96 second. The table shows the relation between cy and the
ramp-up time.
cy ramp time
1 60 milliseconds
2 120
3 180
4 ...
20 1.2 seconds
etc.
Note that a smaller step size would give more steps in the ramp (smoother
operation?), but there would not be as many choices for the total ramp
time.
regards,
Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com
>ian asked:
>>> what i need is to supply the valves with a ramping voltage from
>>> 0v - 10v to start them running and an opposite ramp at the end of their
>>> travel (or just prior to the end actually).
>>> ive been playing with r/c circuits with partial success but would like
>>> the ramp to be more linear. any ideas out there?
>>> the ramp up/down time should be from 0 to 1 second (adjustable).
>Bruce suggested:
>> PWM pin, duty, cycles...
>
>Just to expand a bit on Bruce's suggestion to use PWM: The command would
>have to be enclosed in a loop in order to ramp up the voltage. The PWM must
>be filtered with an RC circuit, feeding a buffer amplifier up to the
>desired 10 volt level.
>
> ' enter with P0 low, off
> cy=16 ' set the ramp-up rate
> for dt=0 to 255 step 5 ' ramp up on P0
> PWM 0,dt,cy ' gradually increase duty cycle
> next
> high 0 ' keep it high
>
>One cycle takes 1.15 millisecond (the manual says "approximately" one
>millisecond). For the record, the maximum value of cycles is 255 (The
>manual says 65535, but that is just wrong.)
Tracy -
Nice catch on the 65535 vs. 255 - but think about it - it may be a bug.
If so, it's a too short compare technique. Alternatively, it's a typo.
Only the code_owner knows for sure <g> !
Amazing what one can "see" when one brain operates like a CPU/ALU
(how sick I am <sigh>). I think I've been doing this ALL TOO LONG !
Thanks for coming to our "rescue".
Regards,
Bruce
>
>The above for-next loop has 52 steps, and takes 52*1.15=60 milliseconds
>when the value of cy=1. Enter the loop with cy=16 and ramp up from 0 volts
>to 5 volts in 0.96 second. The table shows the relation between cy and the
>ramp-up time.
>
> cy ramp time
> 1 60 milliseconds
> 2 120
> 3 180
> 4 ...
> 20 1.2 seconds
> etc.
>
>Note that a smaller step size would give more steps in the ramp (smoother
>operation?), but there would not be as many choices for the total ramp
>time.
>
> regards,
>
> Tracy Allen
> Electronically Monitored Ecosystems
> http://www.emesystems.com
>
>
>
>
>
My Stamp manual v1.9 claims 255 PWM max cycles for the BS1, and 65535 for
BS2. Are you saying the 255 applies to both?
Thanks,
Ray McArthur
Original Message
From: Tracy Allen <emesys@c...>
To: <basicstamps@egroups.com>
Sent: Saturday, April 08, 2000 1:30 AM
Subject: Re: [noparse][[/noparse]basicstamps] voltage ramp
> ian asked:
> >> what i need is to supply the valves with a ramping voltage from
> >> 0v - 10v to start them running and an opposite ramp at the end of
their
> >> travel (or just prior to the end actually).
> >> ive been playing with r/c circuits with partial success but would like
> >> the ramp to be more linear. any ideas out there?
> >> the ramp up/down time should be from 0 to 1 second (adjustable).
> Bruce suggested:
> > PWM pin, duty, cycles...
>
> Just to expand a bit on Bruce's suggestion to use PWM: The command would
> have to be enclosed in a loop in order to ramp up the voltage. The PWM
must
> be filtered with an RC circuit, feeding a buffer amplifier up to the
> desired 10 volt level.
>
> ' enter with P0 low, off
> cy=16 ' set the ramp-up rate
> for dt=0 to 255 step 5 ' ramp up on P0
> PWM 0,dt,cy ' gradually increase duty cycle
> next
> high 0 ' keep it high
>
> One cycle takes 1.15 millisecond (the manual says "approximately" one
> millisecond). For the record, the maximum value of cycles is 255 (The
> manual says 65535, but that is just wrong.)
>
> The above for-next loop has 52 steps, and takes 52*1.15=60 milliseconds
> when the value of cy=1. Enter the loop with cy=16 and ramp up from 0
volts
> to 5 volts in 0.96 second. The table shows the relation between cy and
the
> ramp-up time.
>
> cy ramp time
> 1 60 milliseconds
> 2 120
> 3 180
> 4 ...
> 20 1.2 seconds
> etc.
>
> Note that a smaller step size would give more steps in the ramp (smoother
> operation?), but there would not be as many choices for the total ramp
> time.
>
> regards,
>
> Tracy Allen
> Electronically Monitored Ecosystems
> http://www.emesystems.com
>
>
>
>
couple of questions though.
1. to ramp back down do i just reverse the procedure?
2. there are 2 valves that run simultaneously but may have (probably
will have) different stopping times. seems to me i would have to have
a seperate stamp to monitor each one as if one is being ramped down the
stamp would miss the second. am i right?
p.s thanks bruce for your input
Original Message
From: Tracy Allen <emesys@c...>
To: INTERNET:basicstamps@egroups.com <basicstamps@egroups.com>
Date: Saturday, April 08, 2000 5:31 PM
Subject: Re: [noparse][[/noparse]basicstamps] voltage ramp
>ian asked:
>>> what i need is to supply the valves with a ramping voltage from
>>> 0v - 10v to start them running and an opposite ramp at the end of their
>>> travel (or just prior to the end actually).
>>> ive been playing with r/c circuits with partial success but would like
>>> the ramp to be more linear. any ideas out there?
>>> the ramp up/down time should be from 0 to 1 second (adjustable).
>Bruce suggested:
>> PWM pin, duty, cycles...
>
>Just to expand a bit on Bruce's suggestion to use PWM: The command would
>have to be enclosed in a loop in order to ramp up the voltage. The PWM must
>be filtered with an RC circuit, feeding a buffer amplifier up to the
>desired 10 volt level.
>
> ' enter with P0 low, off
> cy=16 ' set the ramp-up rate
> for dt=0 to 255 step 5 ' ramp up on P0
> PWM 0,dt,cy ' gradually increase duty cycle
> next
> high 0 ' keep it high
>
>One cycle takes 1.15 millisecond (the manual says "approximately" one
>millisecond). For the record, the maximum value of cycles is 255 (The
>manual says 65535, but that is just wrong.)
>
>The above for-next loop has 52 steps, and takes 52*1.15=60 milliseconds
>when the value of cy=1. Enter the loop with cy=16 and ramp up from 0 volts
>to 5 volts in 0.96 second. The table shows the relation between cy and the
>ramp-up time.
>
> cy ramp time
> 1 60 milliseconds
> 2 120
> 3 180
> 4 ...
> 20 1.2 seconds
> etc.
>
>Note that a smaller step size would give more steps in the ramp (smoother
>operation?), but there would not be as many choices for the total ramp
>time.
>
> regards,
>
> Tracy Allen
> Electronically Monitored Ecosystems
> http://www.emesystems.com
>
>
>
>
>
> My Stamp manual v1.9 claims 255 PWM max cycles for the BS1, and 65535 for
> BS2. Are you saying the 255 applies to both?
Hi Ray,
Yes. Cycles=257 gives the same result as cycles=1. The unique values
for cycles are 0 to 255 for both the BS1 and BS2.
For the curious, if cycles=0, pin becomes an input, but it does not
generate any PWM.
Duty goes from 0 to 255, and the duty cycle is 0/256 to 255/256. The
manual has 255 in the denominator, implying that you can get 100% duty
cycle, but the maximum duty cycle is 255/256. "HIGH pin" ==> 100% duty
cycle!
-- Tracy
Yes, the following should take it up in a one second ramp, hold one second,
and then down in a one second ramp, hold one second, and repeat. 52 steps
in each ramp:
cy=16 ' set the ramp rate
loop:
for dt=0 to 255 step 5 ' ramp up voltage on P0
PWM 0,dt,cy ' gradually increase duty cycle
next
high 0 ' keep it high
pause 1000 ' wait a second
for dt=255 to 0 step 5 ' ramp down on P0
PWM 0,dt,cy ' gradually decrease duty cycle
next
low 0 ' keep it low
pause 1000 ' wait a second
goto loop ' repeat
> 2. there are 2 valves that run simultaneously but may have (probably
> will have) different stopping times. seems to me i would have to have
> a seperate stamp to monitor each one as if one is being ramped down the
> stamp would miss the second. am i right?
Need more info. What determines when they have to work? Fixed schedule?
Feedback from switch? Maybe it could be done as a state machine. Or an
external circuit for the ramp.
-- Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com
>> will have) different stopping times. seems to me i would have to have
>> a seperate stamp to monitor each one as if one is being ramped down the
>> stamp would miss the second. am i right?
>
>Need more info. What determines when they have to work? Fixed schedule?
>Feedback from switch? Maybe it could be done as a state machine. Or an
>external circuit for the ramp.
>
> -- Tracy Allen
> Electronically Monitored Ecosystems
> http://www.emesystems.com
>
The basic idea is that this section of the machine is controlled by its
own bs2. The sequence of events as originally visualised is :-
1. the bs2 is told by the master bs2 to shift the 2 workheads to a
predetermined point along the tracks (both left and right).
2. the bs2 then turns on the main flow valves via relays to the appropriate
direction. at this point nothing moves as oil flow cannot get past the
proportional valves as they are still in the off state.
3. at this point i envisaged the bs2 would set latching relays which in
turn would start ramp up circuits which would begin the flow through the
prop. valves.
4. the workheads would then begin to accelerate up to speed.
5. on the heads would be mounted 2 micro switches.
1 to shut off the prop. latches, thereby begining the ramp down
sequence (and hence decelerating the head).
the 2nd switch would then hit a stop at some point during the ramp down
period, prefferably near the end of the ramp, thus cutting the main flow
valve off, stopping the head at the right place (we hope).
everything is now back to square 1 and the bs2 has received confirmation
via the stop switches that the heads have reached their destinations. this
may happen at slightly different times depending on which head is faster or
may have to travel a greater distance than the other.
thats about as simple as i can put it.
separate ramp circuits would make this easy or else i replace the bs2 with
2 bs1's.
what do you think?
regards
ian
>
The way I understand what is happening, both arms of your machine will
start up at the same time, but each arm will come to its slowdown point and
its stop point at different times. Using a separate BS1 for each arm would
certainly be a viable option.
Just to explore the possibility of doing it with a single Stamp2, here is a
crude implementation as a state machine. The "ramp" routine would be
called when it is time to get both arms moving. Even tho both arms start
up at the same time, the slow-down point and the stop point are determined
independently by the state of the microswitches attached to:
slowdown for arm 1 when in4=0
stop for arm1 when in5=0
slowdown for arm 2 when in6=0
stop for arm2 when in7=0
and two more state variables for the duty ratio of the PWM
dt1 for arm1
dt2 for arm2
The routine returns when both arms are in the stop state.
ramp:
dt1=0
dt2=0
cy=8 ' sets the ramp rate cycles of PWM
ramp1:
PWM 1,dt1,cy ' arm 1 on P1
PWM 2,dt2,cy ' arm 2 on P2
dt1=(in4*2-1)*5+dt1*dt1*in5 max 250 min 10
dt2=(in6*2-1)*5+dt2*dt2*in7 max 250 min 10
if in5|in7 then ramp1 ' repeat until both stops
return
So you see it is not too much code. The cycles=8 and the increment of
duty=5 make the ramp approx 1 second long. The dt state variable require
explanation.
(in4*2-1)*5 returns a value of +5 when in4=1, and -5 when in4=0
(in4*2-1)*5+dt1 adds or subtracts 5 from the current value of dt1,
ramping up or down depending on the state of in4
(in4*2-1)*5+dt1*dt1 prevents the result from becoming less than zero
(in4*2-1)*5+dt1*dt1*in5 brings the result to zero abruptly when it hits
the stop, even if there is some residual voltage.
(in4*2-1)*5+dt1*dt1*in5 max 250 prevents the PWM value from exceeding
250
(in4*2-1)*5+dt1*dt1*in5 max 250 min 10 assures that it will eventually
arrive at the stop.
Same scheme, independent for arm 2. The ramp-down rate has to be fine
tuned so that there will not be much residual motion left when the arm hits
the stop; but on the other hand, it has to have enough motion to reach the
stop. The program as it stands does not do any adjustment. One way cool
approach would be to make duty and cycles adaptive, so that the program
teaches itself the parameters it needs to get the best possible motion.
That would be based on the residual count left when it hits the stop.
Fuzzy AI rather than PID.
regards,
Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com
---original message---->
"Ian Lawson" <irlawson@i...>:
The basic idea is that this section of the machine is controlled by its
own bs2. The sequence of events as originally visualised is :-
1. the bs2 is told by the master bs2 to shift the 2 workheads to a
predetermined point along the tracks (both left and right).
2. the bs2 then turns on the main flow valves via relays to the
appropriate
direction. at this point nothing moves as oil flow cannot get past the
proportional valves as they are still in the off state.
3. at this point i envisaged the bs2 would set latching relays which in
turn would start ramp up circuits which would begin the flow through the
prop. valves.
4. the workheads would then begin to accelerate up to speed.
5. on the heads would be mounted 2 micro switches.
1 to shut off the prop. latches, thereby begining the ramp down
sequence (and hence decelerating the head).
the 2nd switch would then hit a stop at some point during the ramp down
period, prefferably near the end of the ramp, thus cutting the main flow
valve off, stopping the head at the right place (we hope).
everything is now back to square 1 and the bs2 has received confirmation
via the stop switches that the heads have reached their destinations. this
may happen at slightly different times depending on which head is faster or
may have to travel a greater distance than the other.
thats about as simple as i can put it.
separate ramp circuits would make this easy or else i replace the bs2
with
2 bs1's.
what do you think?
I cant thank you enough for the effort you have put into this question.
If i may impose upon your good nature one more time, ihave one other small
query.
I need to interface the stamp(s) to the valves.
the solenoids actually run on 12v as does the rest of the machine, however
the electronics embedded in the plugs require the 0v-10v ramp. i only need
to apply the ramp at some milliamps as the plug will take care of the amps
needed to run the solenoid.
Could i use say a variation of the circuit on page 56 of the stamp manaul or
is there a better way?
Thanks
Ian
Original Message
From: Tracy Allen <emesys@c...>
To: INTERNET:basicstamps@egroups.com <basicstamps@egroups.com>
Date: Wednesday, April 12, 2000 6:00 AM
Subject: Re: [noparse][[/noparse]basicstamps] voltage ramp
>Hi Ian,
>
>The way I understand what is happening, both arms of your machine will
>start up at the same time, but each arm will come to its slowdown point and
>its stop point at different times. Using a separate BS1 for each arm would
>certainly be a viable option.
>
>Just to explore the possibility of doing it with a single Stamp2, here is a
>crude implementation as a state machine. The "ramp" routine would be
>called when it is time to get both arms moving. Even tho both arms start
>up at the same time, the slow-down point and the stop point are determined
>independently by the state of the microswitches attached to:
> slowdown for arm 1 when in4=0
> stop for arm1 when in5=0
> slowdown for arm 2 when in6=0
> stop for arm2 when in7=0
>and two more state variables for the duty ratio of the PWM
> dt1 for arm1
> dt2 for arm2
>The routine returns when both arms are in the stop state.
>
>
>ramp:
> dt1=0
> dt2=0
> cy=8 ' sets the ramp rate cycles of PWM
>ramp1:
> PWM 1,dt1,cy ' arm 1 on P1
> PWM 2,dt2,cy ' arm 2 on P2
> dt1=(in4*2-1)*5+dt1*dt1*in5 max 250 min 10
> dt2=(in6*2-1)*5+dt2*dt2*in7 max 250 min 10
> if in5|in7 then ramp1 ' repeat until both stops
>return
>
>So you see it is not too much code.
> solenoids actually run on 12v as does the rest of
> the machine, however the electronics embedded in the
> plugs require the 0v-10v ramp. i only need to apply
> the ramp at some milliamps as the plug will take care
> of the amps needed to run the solenoid. Could i use say
> a variation of the circuit on page 56 of the stamp manaul
> or is there a better way?
You mean the "Op-amp buffer for PWM"? That would be fine. Not necessarily
the CA5160 op-amp. Modern cmos op-amps will give more better performance
with fewer components. x2 gain is needed to get up to 10 volts.
100k 3|\ 1/2 LMC6082 or LTC1051
P1-/\/\--o
|+\
PWM | | >1
o-/\/\- plug
===== ;--|-/ |
| .1 | 2|/|4 | gain=x2
| | Vss |
Vss--o--/\/\-o
/\/\--'
100k 100k
Experiment with the time-constant of the input RC. I think 5-10
milliseconds would be okay. The op-amps mentioned are dual cmos precision
types with low input offset (no adjustment necessary) and unity gain
stable.
-- Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com
what voltage does the op amp run on and what value resistor to the plug?
regards
Ian
Original Message
From: Tracy Allen <emesys@c...>
To: INTERNET:basicstamps@egroups.com <basicstamps@egroups.com>
Date: Wednesday, April 12, 2000 12:42 PM
Subject: Re: [noparse][[/noparse]basicstamps] voltage ramp
>
>You mean the "Op-amp buffer for PWM"? That would be fine. Not necessarily
>the CA5160 op-amp. Modern cmos op-amps will give more better performance
>with fewer components. x2 gain is needed to get up to 10 volts.
>
> 100k 3|\ 1/2 LMC6082 or LTC1051
> P1-/\/\--o
|+\
> PWM | | >1
o-/\/\- plug
> ===== ;--|-/ |
> | .1 | 2|/|4 | gain=x2
> | | Vss |
> Vss--o--/\/\-o
/\/\--'
> 100k 100k
>
>Experiment with the time-constant of the input RC. I think 5-10
>milliseconds would be okay. The op-amps mentioned are dual cmos precision
>types with low input offset (no adjustment necessary) and unity gain
>stable.
>
> -- Tracy Allen
> Electronically Monitored Ecosystems
> http://www.emesystems.com
>
>
>
>
> what voltage does the op amp run on and what value resistor to the plug?
Vdd=11-13 volts
|
100k 3|\|8 1/2 LMC6082 or LTC1051
P1-/\/\--o
|+\
PWM | | >1
o-/\/\- plug
===== ;--|-/ | 100
| .1 | 2|/|4 | gain=x2
| | Vss |
Vss--o--/\/\-o
/\/\--'
100k 100k
Either of these amplifiers can swing up almost to the + rail, depending on
how much current has to go to the plug. So with 10 volts needed to the
plug, a 12 volt power supply should be fine. With these particular
op-amps, do not go over 15 volts. The resistor to the plug is only for
circuit protection and isolation. Make it 100 ohms, or just leave it out.
Are there any long cables between the op-amp and the plug? If so, the
resistor may be necessary.
These op-amps are chosen for high input resistance, and great DC accuracy;
100 microvolts offset for the LMC6082 and 10 microvolts for the LTC1051.
Also input range includes ground, output is rail to rail. But you could
probably get by with a cheap jellybean LM358. It has to be a single supply
op-amp.
-- Tracy
got it breadboarded up and its ramping its head off.
thanks again for your help.
ian
Original Message
From: Tracy Allen <emesys@c...>
To: INTERNET:basicstamps@egroups.com <basicstamps@egroups.com>
Date: Thursday, April 13, 2000 12:28 PM
Subject: Re: [noparse][[/noparse]basicstamps] voltage ramp
>> Two things:-
>> what voltage does the op amp run on and what value resistor to the plug?
>
> Vdd=11-13 volts
> |
> 100k 3|\|8 1/2 LMC6082 or LTC1051
> P1-/\/\--o
|+\
> PWM | | >1
o-/\/\- plug
> ===== ;--|-/ | 100
> | .1 | 2|/|4 | gain=x2
> | | Vss |
> Vss--o--/\/\-o
/\/\--'
> 100k 100k
>
>Either of these amplifiers can swing up almost to the + rail, depending on
>how much current has to go to the plug. So with 10 volts needed to the
>plug, a 12 volt power supply should be fine. With these particular
>op-amps, do not go over 15 volts. The resistor to the plug is only for
>circuit protection and isolation. Make it 100 ohms, or just leave it out.
>Are there any long cables between the op-amp and the plug? If so, the
>resistor may be necessary.
>
>These op-amps are chosen for high input resistance, and great DC accuracy;
>100 microvolts offset for the LMC6082 and 10 microvolts for the LTC1051.
>Also input range includes ground, output is rail to rail. But you could
>probably get by with a cheap jellybean LM358. It has to be a single supply
>op-amp.
>
> -- Tracy
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