Photoresistor triggered solenoid, need help

[[email protected]]

Alright, you've all confused me to some degree =) I'm not sure there
was a consensus as to which of the above circuits will work. I favor
simple ones as I mentioned before, I'm rather ignorant and
unexperienced with most of this stuff.

All the parts I currently have are from RadioShack which is where I'll
ideally get any further needed parts because they're close by and I
don't have to order them. The transistors I have are a 2N4401 and a
package of these generic switching transistors ...
http://www.radioshack.com/product/i...2586&cp=&pg=2&kw=transistor&parentPage=search

I'm ready to run out and get any additional parts I need and build this
bad boy, let me know which one I should take a crack at first. Thanks
again for so much help!

 

[Fred Bloggs]

I am trying to design/build a simple circuit

to test a software application I am developing. I have a 12v solenoid
that I want to fire/push when I light up a certain area of the monitor.
I was hoping to use a photoresistor which I can tape to the
monitor. I
have an assortment of 5 but the one I was trying to use has a
resistance of 800 ohms when the monitor is lit and 12k ohms when the
monitor is dark.
Can anybody suggest some approaches or even better design a simple
circuit that I could use to do what I described.
Summary of current parts, I can purchase additional ones if needed:
12V/3A power supply
CdS Photoresistor (800 in light, 12k in dark)
NPN transistors
741 Opamp chip
12V solenoid (30Watt power rating)


<SNIP>

The solenoid driver portion:
.
. .------------------------------+-------+-----+------.
. (+)-----+------+----. | | | |
. | | | | | | |
. | |\|741 | | S | |
. | | \ | | S [3.3,1/2W] |
. | | >--------[470]-. | S | |
. | | / | | | S | |
.12VDC | |/| [2.7K] .|>|-+ [39/5W] S | |
. +| | | |914 | | | | |
. === | | | |< | | | |
. 100U | +-----+--|2N2907A | | | |
. | | | |\ | +-|>|-' |
. | | | | |/ | 3A,100V +|
. | | | +-----|2N3055 | ===
. | | | | |> | 10U
. | | [1K] [2.2K] | |/ |
. | | | | +-----| 2N3055 |
. (-)-----+------+----+----------' | |> |
. | [100] | |
. | | | |
. '------------------------------+-------+------------+
.

What's with all the 2N3055s? Surely a power mosfet would be better -
you could drive it straight from the 741. Perhaps with a pulldown or
use a LM358 instead, to make sure it turns off.

Geez- thanks for the inside scoop)

I just knew you'd appreciate my pearls of wisdom there

I don't see power MOSFETs in the OP's parts list lineup
though.

No reason to suspect his "NPN"s are 2N3055's either though, right? If
he is going to have to buy a suitable transistor anyway, perhaps there
are better choices.

...2N3055s are available from RS and the overhead is only 10% of his
solenoid dissipation. The only RS MOSFET, the IRF510, is unsuitable
and they are $2 each.

Hmm... why is it unsuitable (technically)? Seems like it should
work. How much do all those transistors add up to, plus that 5W
resistor if he can get it?

The IRF510 has a typical RDS,ON of 0.5 ohm at VGS=10V for a
P=2.5^2*0.5=3.0W and a drive level loss of 1.25V or 10%. The 2N3055 will
have P=IB*VBE+IC*VCE=0.25*1+2.5*0.15=0.625W with a drive level loss of
1%. Assuming you have a choice of 2x 2N3055 or 2x IRF510, then the
parallel combo of the 2x FETs still has a total P=1.6W and 5% drive
level loss. RS has 10W 10, 50 and 100 ohm wirewounds he can
series-parallel for 38 ohms.

 

[Fred Bloggs]

Just use this:
http://www.radioshack.com/product/i...PAD/Product+Type/SPST&fbc=1&parentPage=family

 

[ehsjr]

John Devereux wrote:



I am trying to design/build a simple circuit


to test a software application I am developing. I have a 12v solenoid
that I want to fire/push when I light up a certain area of the
monitor.
I was hoping to use a photoresistor which I can tape to the
monitor. I
have an assortment of 5 but the one I was trying to use has a
resistance of 800 ohms when the monitor is lit and 12k ohms when the
monitor is dark.
Can anybody suggest some approaches or even better design a simple
circuit that I could use to do what I described.
Summary of current parts, I can purchase additional ones if needed:
12V/3A power supply
CdS Photoresistor (800 in light, 12k in dark)
NPN transistors
741 Opamp chip
12V solenoid (30Watt power rating)


<SNIP>

The solenoid driver portion:
.
. .------------------------------+-------+-----+------.
. (+)-----+------+----. | | | |
. | | | | | | |
. | |\|741 | | S | |
. | | \ | | S [3.3,1/2W] |
. | | >--------[470]-. | S | |
. | | / | | | S | |
.12VDC | |/| [2.7K] .|>|-+ [39/5W] S | |
. +| | | |914 | | | | |
. === | | | |< | | | |
. 100U | +-----+--|2N2907A | | | |
. | | | |\ | +-|>|-' |
. | | | | |/ | 3A,100V +|
. | | | +-----|2N3055 | ===
. | | | | |> | 10U
. | | [1K] [2.2K] | |/ |
. | | | | +-----| 2N3055 |
. (-)-----+------+----+----------' | |> |
. | [100] | |
. | | | |
. '------------------------------+-------+------------+
.


What's with all the 2N3055s? Surely a power mosfet would be better -
you could drive it straight from the 741. Perhaps with a pulldown or
use a LM358 instead, to make sure it turns off.


Geez- thanks for the inside scoop)

I just knew you'd appreciate my pearls of wisdom there

I don't see power MOSFETs in the OP's parts list lineup
though.

No reason to suspect his "NPN"s are 2N3055's either though, right? If
he is going to have to buy a suitable transistor anyway, perhaps there
are better choices.

...2N3055s are available from RS and the overhead is only 10% of his
solenoid dissipation. The only RS MOSFET, the IRF510, is unsuitable
and they are $2 each.

Hmm... why is it unsuitable (technically)? Seems like it should
work. How much do all those transistors add up to, plus that 5W
resistor if he can get it?

The IRF510 has a typical RDS,ON of 0.5 ohm at VGS=10V for a
P=2.5^2*0.5=3.0W and a drive level loss of 1.25V or 10%. The 2N3055 will
have P=IB*VBE+IC*VCE=0.25*1+2.5*0.15=0.625W with a drive level loss of
1%. Assuming you have a choice of 2x 2N3055 or 2x IRF510, then the
parallel combo of the 2x FETs still has a total P=1.6W and 5% drive
level loss. RS has 10W 10, 50 and 100 ohm wirewounds he can
series-parallel for 38 ohms.

Rat Shack also sells a TIP120 which he could drive directly
from the 470 on the output of the 741 to operate the solenoid.

Ed

 

[John Devereux]

John Devereux wrote:



I am trying to design/build a simple circuit

to test a software application I am developing. I have a 12v solenoid
that I want to fire/push when I light up a certain area of the monitor.
I was hoping to use a photoresistor which I can tape to the
monitor. I
have an assortment of 5 but the one I was trying to use has a
resistance of 800 ohms when the monitor is lit and 12k ohms when the
monitor is dark.
Can anybody suggest some approaches or even better design a simple
circuit that I could use to do what I described.
Summary of current parts, I can purchase additional ones if needed:
12V/3A power supply
CdS Photoresistor (800 in light, 12k in dark)
NPN transistors
741 Opamp chip
12V solenoid (30Watt power rating)


<SNIP>

The solenoid driver portion:
.
. .------------------------------+-------+-----+------.
. (+)-----+------+----. | | | |
. | | | | | | |
. | |\|741 | | S | |
. | | \ | | S [3.3,1/2W] |
. | | >--------[470]-. | S | |
. | | / | | | S | |
.12VDC | |/| [2.7K] .|>|-+ [39/5W] S | |
. +| | | |914 | | | | |
. === | | | |< | | | |
. 100U | +-----+--|2N2907A | | | |
. | | | |\ | +-|>|-' |
. | | | | |/ | 3A,100V +|
. | | | +-----|2N3055 | ===
. | | | | |> | 10U
. | | [1K] [2.2K] | |/ |
. | | | | +-----| 2N3055 |
. (-)-----+------+----+----------' | |> |
. | [100] | |
. | | | |
. '------------------------------+-------+------------+
.

What's with all the 2N3055s? Surely a power mosfet would be better -
you could drive it straight from the 741. Perhaps with a pulldown or
use a LM358 instead, to make sure it turns off.


Geez- thanks for the inside scoop)

I just knew you'd appreciate my pearls of wisdom there

I don't see power MOSFETs in the OP's parts list lineup
though.

No reason to suspect his "NPN"s are 2N3055's either though, right?
If
he is going to have to buy a suitable transistor anyway, perhaps there
are better choices.

...2N3055s are available from RS and the overhead is only 10% of his
solenoid dissipation. The only RS MOSFET, the IRF510, is unsuitable
and they are $2 each.

Hmm... why is it unsuitable (technically)? Seems like it should
work. How much do all those transistors add up to, plus that 5W
resistor if he can get it?

The IRF510 has a typical RDS,ON of 0.5 ohm at VGS=10V for a
P=2.5^2*0.5=3.0W and a drive level loss of 1.25V or 10%. The 2N3055
will have P=IB*VBE+IC*VCE=0.25*1+2.5*0.15=0.625W with a drive level
loss of 1%. Assuming you have a choice of 2x 2N3055 or 2x IRF510, then
the parallel combo of the 2x FETs still has a total P=1.6W and 5%
drive level loss. RS has 10W 10, 50 and 100 ohm wirewounds he can
series-parallel for 38 ohms.

You seem to be igoring the power loss from your 5W resistors, itself
about the ~3W of the (single) IRF510 solution.

 

[Fred Bloggs]

You seem to be igoring the power loss from your 5W resistors, itself
about the ~3W of the (single) IRF510 solution.

I already said that the overhead is about 10%, the above comparison was
between components in the load circuit path. It's just a dumb hobby circuit.

 

[[email protected]]

I built the following circuit from T.Wilkins:

+12V o---------+-------+-----+
| | |
| | |
| C |
| O |
| I |
| L |
[Cds] | |
| | |
| +-|>|-|
| |
| +--+
| | |
| |/ | Q2
+--| | 2N2904
| |> |
| | |/ Q1
+-| 2N3055
| |>
R1 [330] |
| |
gnd o----------+--------+


It seemed to be working, switching the solenoid on and off when I
covered and uncovered the CdS with my finger. When I taped the CdS to
the monitor and began the test however the 2N3904 Transistor fried out.
Is there a better replacement for that transistor that I could just pop
inplace of the burnt out one?

 

[[email protected]]

I copied the circuit from the original post and thus copied the same
typo, doh! Q2 is the 2N3904 which fried.

 

[Rich Grise]

The concept is to take the 741 and use a pair of resistors from 12V to
Ground to make are referance voltage which is connected to one input on the
741. Use the photoresistor and a fixed resistor to make voltage the goes
above the and below the referance voltage as the light is on and off.

The output of the op amp will go hi or lo as the light goes on and off. use
the op amp out to drive the transistor thru a resistor to the base, connect
the emitter to ground and the collector to the solenoid with the other end
of the solenoid to +12V. Put a diode across the solenoid with the cathode to
the +12 to prevent the inductive kick when from the solenoid when it is
turned off from destroying the transistor.

You might have to swap inputs to the 741 to make the solenoid On and Off
under the correct conditions.

Dan

He'll also need to use more than just the one transistor, for the 2.5A
that the solenoid draws.

And add a little positive feedback, to give it some hysteresis, so it
doesn't oscillate.

Thanks,
Rich

 

[[email protected]]

Woo ha! I replaced the friend 2N3904 with a TIP3055 and everything is
working. I'm getting near constant response times as well which is
great. Thanks again to everyone for all the help.

 

[T. Wilkins]

Woo ha! I replaced the friend 2N3904 with a TIP3055 and everything is
working. I'm getting near constant response times as well which is
great. Thanks again to everyone for all the help.

Glad it finally works!
The dissipation was still too great for the 2N3904. A TIP3055 as a driver
may be a bit overkilled but if it's fine this way, why not!

Tim

 

[Fred Bloggs]

I built the following circuit from T.Wilkins:

+12V o---------+-------+-----+
| | |
| | |
| C |
| O |
| I |
| L |
[Cds] | |
| | |
| +-|>|-|
| |
| +--+
| | |
| |/ | Q2
+--| | 2N2904
| |> |
| | |/ Q1
+-| 2N3055
| |>
R1 [330] |
| |
gnd o----------+--------+


It seemed to be working, switching the solenoid on and off when I
covered and uncovered the CdS with my finger. When I taped the CdS to
the monitor and began the test however the 2N3904 Transistor fried out.
Is there a better replacement for that transistor that I could just pop
inplace of the burnt out one?

You can try using another 2N3055, a TIP31, or TIP41 for Q2, all
available at RS.

 

[Fred Bloggs]

Woo ha! I replaced the friend 2N3904 with a TIP3055 and everything is
working. I'm getting near constant response times as well which is
great. Thanks again to everyone for all the help.

You don't look so bright using that slipshod thing. At a minimum you can
do something like this:
View in a fixed-width font such as Courier.

..
..
.. +12V
.. |
.. .----------+--------------------------+----.
.. | | | |
.. | | | S
.. | | K S
.. | | 555 A S
.. [2.7K] ---------- | S
.. | | V+/RST | | |
.. | | CNT|-N/C '----+
.. | | | |
.. | | | .--[100]-+-[100]--. |
.. +-----|THRESH | | | | |/ |-
.. | | OUT|-+--[100]-+-[100]--+---| |-
.. +-----|TRIG | |> |-
.. | | | 4X 1/2W 2N3055 |
.. | | GND | | HEATSINK
.. CdS ---------- |
.. | | |
.. | | |
.. '----------+-------------------------------'
.. |
.. ---
.. ///
..
..
..
..

 

[ehsjr]

I copied the circuit from the original post and thus copied the same
typo, doh! Q2 is the 2N3904 which fried.

You can use a TIP120 available from radio shack.

Ed

 

[Fred Bloggs]

You can use a TIP120 available from radio shack.

Ed

All of these Darlingtons are cooking at over 2-2.5W Pd.

 

[T. Wilkins]

Woo ha! I replaced the friend 2N3904 with a TIP3055 and everything is
working. I'm getting near constant response times as well which is
great. Thanks again to everyone for all the help.

You don't look so bright using that slipshod thing. At a minimum you can
do something like this:
View in a fixed-width font such as Courier.

.
.
. +12V
. |
. .----------+--------------------------+----.
. | | | |
. | | | S
. | | K S
. | | 555 A S
. [2.7K] ---------- | S
. | | V+/RST | | |
. | | CNT|-N/C '----+
. | | | |
. | | | .--[100]-+-[100]--. |
. +-----|THRESH | | | | |/ |-
. | | OUT|-+--[100]-+-[100]--+---| |-
. +-----|TRIG | |> |-
. | | | 4X 1/2W 2N3055 |
. | | GND | | HEATSINK
. CdS ---------- |
. | | |
. | | |
. '----------+-------------------------------'
. |
. ---
. ///
.
.

The guy was just asking something "simple"...
He may be quite satisfied with this design and, from this, he may be
interested to go further and experiments with more elaborate designs.

But using the ubiquitous 555 which have the drive capability and also
hysterisis is clever.

Tim

 

[ehsjr]

All of these Darlingtons are cooking at over 2-2.5W Pd.

Yup. The 120 needs a heatsink, or you need to keep its
dissipation under 2W.

Ed