Driver circuit. How do you figure out what transistor and resistor values to use? Need help

[Chris]

Thank you guys so much for your help so far!

I'm sorry that i seem to be ignorant (which i am) and slow (that too)
and i don't quite understand all of which you guys are trying to
explain to me. I don't really describe my problems well either. so
thanks alot for your patience.

The reason why i laid out my problems in parts, is because i thought it
would be easier for me to solve one step at a time. I apologise for the
trouble i caused.

So i shall now try to summarize everything.

For my project, I am supposed to embed an LLE sensor which will sound a
buzzer when the liquid reaches that certain level in the mug. A temp
sensor, or thermistor, which will sound the buzzer (I think it's
another buzzer, my teacher did not clarify this with me) if the liquid
is too hot. And lastly, a tilt sensor, which will either 1. turn off
the LLE and temp sensor or 2. turn off the buzzer when the mug is in a
tilted position.

My 1st problem was not knowing how to get a suitable buffer/driver
circuit to connect the LLE sensor and buzzer. But from all your help, i
have decided to use the PNP with the 2 10k resistors. If that works
best.

Now i have to figure out how to connect everything together and make it
work as a single unit. I have yet to find a suitable temp
sensor/thermistor or tilt sensor.

Btw, I'm sorry not to have mentioned this, but i only noticed it
yesterday when i was testing the LLE sensor. The LLE sensor has 4
wires, not 3. REd, blue, green and black. What the heck is the black
one for? I hope this doesn't create another problem.

erm.. is this laying out of my problem better?

Lastly, what is an OP? Does it refer to me? If it does.. I'm a her not
a he. -smiles-

Thank you so so much!!

Hello again. First off, you don't seem to have a Honeywell LLE sensor
after all. I believe they make six different models, all of which have
identical electrical circuits and only three wires. The differences
are solely in housing types for different applications.

I think you've got a Honeywell LL-type sensor, which accounts for the
four wires. They make nine different kinds of LL-type sensors, and I
believe all of them are electrically the same and have 4 wires. The
Honeywell datasheets are typically inscrutable, but the installation
guides are usually a bit better. I've never been happy with Honeywell
industrial documentation on anything they make, I'm afraid. Usually
that would be a killer, but they happen to make really good stuff, for
the most part. That makes up for it, and their distributors can
usually answer any questions eventually. Look at this:

http://content.honeywell.com/sensing/prodinfo/liquidlevel/installation/xp4025-1.pdf

It shows a device that operates on a 5VDC to 16VDC supply, and has an
internal voltage regulator. The functions of the four wires on the
LL-type sensors are as follows:

* Red Vcc (+5VDC to +16VDC)
* Blue 0VDC
* Green Schmitt Trigger Output (internal open-collector transistor
with an internal 10K pullup to Vcc)
* Black To internal LED (use series resistor to Vcc such that I(LED)
= 30mA nominal -- do not exceed 40 mA. I(f)(LED)(typ) = 1.2V

This is kind of a critical problem here. You have to know what you're
working with, unless you want to let the smoke out. However, if you do
have this sensor, your job is now easy:

` VCC VCC VCC
` + + +
` | | |
` .-. | |
` R1| | | .-. VCC
` | | Red| R2| | +
` '-' .----o-----. | | |
` | | | '-' |
` | Black| LL |Green ___ | |<
` '-------o Sensor o-----|___|--o----|2N3906
` | | R2 |\
` | | |
` '----o-----' |
` Blue| |
` | |
` === / \
` GND (BZ1)
` \_/
` |
` |
` ===
` GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

By the way, I believe but can't determine for sure if the output is
active-high or active-low. By that I mean whether the logic level is 1
(Vcc) or 0 (0V) when water is present in front of the sensor. In most
all sensors of this type, it's active-low, and the driver above works
for that (turns the buzzer on when the sensor output goes low).
However, if you want the reverse effect for some reason (buzzer ON when
sensor output is HIGH), or if I'm wrong in my assumption that the
output is active-low, the internal 10K pullup makes your driver circuit
the easiest yet:

` VCC VCC VCC
` + + +
` | | |
` .-. | / \
` R1| | | (BZ1)
` | | Red| \_/
` '-' .----o-----. |
` | | | |
` | Black| LL |Green |/
` '-------o Sensor o------| 2N3904
` | | |>
` | | |
` '----o-----' |
` Blue| ===
` | GND
` ===
` GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

The internal 10K pullup resistor means that when the sensor output is
high, it will source enough current into the base of the NPN transistor
so that it will turn on for a 10mA load quite well.

Since you're supposed to be pulling 30mA for the LEDs, I wouldn't think
a few coin cells would last that long. They're basically intended for
a load of a mA or so at best. You might do better with a 9V
"transistor" battery -- that's more along the lines of what's
considered a normal load for them. The 9V battery will also be cheaper
in the long run -- you can get a lot more power from one of these than
a couple of coin cells.

R1 is used to regulate LED current. The installation sheet suggests
120 ohms, 1/4 watt for a 5V supply. If you're using a 9V battery, you
should have a 270 ohm resistor (1/4 watt is acceptable, 1/2 watt is
preferred). If you've got a 12VDC supply, you should use a 390 ohm,
1/2 watt resistor. R2 (2 ea.) can be 10K, 1/4 watt for all values of
Vcc.

Now, most tilt switches are just normally open mechanical switches,
where either a metal ball or a blob of mercury will close a connection
if the device tilts. You can just connect the normally open switch
from the base to the emitter of the transistor for either of the
diagrams above. That way, when the tilt switch turns on, it will
prevent the transistor (and buzzer) from turning on. Simple. If your
tilt switch is normall closed (the contacts open when the device tilts)
you can either use it to interrupt the power supply to the LL sensor,
or interrupt the flow of current to the base of the transistor. That
works for either of the above diagrams, too. Again, simple.

From your control logic, I'm not sure you actually want the hot alarm

to be disabled when someone's about to scald their lips. So, all we
have to do to complete this is determine what you're going to use as a
temperature sensor. Please post back and let us know what the teacher
suggests, or if you've already bought something.

I can say that sensing temp with a thermistor will require an EXACT
part number. Thermistor resistances are usually specified at room temp
(25C), and have an almost infinite number of different resistance value
vs. temp. graphs. If you have to use a thermistor, you will need to
make a current source to create a voltage across the thermistor
(usually just another transistor and a couple of resistors will
suffice), and an IC comparator to compare the voltage across the
thermistor with a contrived voltage which would represent overtemp. If
the thermistor voltage exceeds the setpoint, the comparator can turn on
and drive another small beeper directly.

As I said in an earlier post, it might be easier for a newbie to spring
for an LM34 IC, which works on 5V to 30VDC as a power supply, and
outputs 10mV per degree. You can then feed that voltage directly into
the comparator without worrying about thermistor curves. You may have
a bit of a problem in that the LM34 looks like a TO-92 transistor and
is not immersible (it will short out your power supply), so you might
have to glue the sensor to the bottom or outside of the cup. Actually,
you usually need to purchase special thermistors which are made with a
watertight sheath, allowing them to be immersed, too. Anyway, you need
to find this stuff out, and get back to us.

You're almost there. Get back to us with more information about
whether you've got an LL-type level sensor, and the type and specific
part number of the temp sensor you need.

Good luck
Chris

 

[obliquez]

Hello again. First off, you don't seem to have a Honeywell LLE sensor
after all. I believe they make six different models, all of which have
identical electrical circuits and only three wires. The differences
are solely in housing types for different applications.

I think you've got a Honeywell LL-type sensor, which accounts for the
four wires. They make nine different kinds of LL-type sensors, and I
believe all of them are electrically the same and have 4 wires. The
Honeywell datasheets are typically inscrutable, but the installation
guides are usually a bit better. I've never been happy with Honeywell
industrial documentation on anything they make, I'm afraid. Usually
that would be a killer, but they happen to make really good stuff, for
the most part. That makes up for it, and their distributors can
usually answer any questions eventually. Look at this:

http://content.honeywell.com/sensing/prodinfo/liquidlevel/installation/xp4025-1.pdf

It shows a device that operates on a 5VDC to 16VDC supply, and has an
internal voltage regulator. The functions of the four wires on the
LL-type sensors are as follows:

* Red Vcc (+5VDC to +16VDC)
* Blue 0VDC
* Green Schmitt Trigger Output (internal open-collector transistor
with an internal 10K pullup to Vcc)
* Black To internal LED (use series resistor to Vcc such that I(LED)
= 30mA nominal -- do not exceed 40 mA. I(f)(LED)(typ) = 1.2V

This is kind of a critical problem here. You have to know what you're
working with, unless you want to let the smoke out. However, if you do
have this sensor, your job is now easy:

` VCC VCC VCC
` + + +
` | | |
` .-. | |
` R1| | | .-. VCC
` | | Red| R2| | +
` '-' .----o-----. | | |
` | | | '-' |
` | Black| LL |Green ___ | |<
` '-------o Sensor o-----|___|--o----|2N3906
` | | R2 |\
` | | |
` '----o-----' |
` Blue| |
` | |
` === / \
` GND (BZ1)
` \_/
` |
` |
` ===
` GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

By the way, I believe but can't determine for sure if the output is
active-high or active-low. By that I mean whether the logic level is 1
(Vcc) or 0 (0V) when water is present in front of the sensor. In most
all sensors of this type, it's active-low, and the driver above works
for that (turns the buzzer on when the sensor output goes low).
However, if you want the reverse effect for some reason (buzzer ON when
sensor output is HIGH), or if I'm wrong in my assumption that the
output is active-low, the internal 10K pullup makes your driver circuit
the easiest yet:

` VCC VCC VCC
` + + +
` | | |
` .-. | / \
` R1| | | (BZ1)
` | | Red| \_/
` '-' .----o-----. |
` | | | |
` | Black| LL |Green |/
` '-------o Sensor o------| 2N3904
` | | |>
` | | |
` '----o-----' |
` Blue| ===
` | GND
` ===
` GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

The internal 10K pullup resistor means that when the sensor output is
high, it will source enough current into the base of the NPN transistor
so that it will turn on for a 10mA load quite well.

Since you're supposed to be pulling 30mA for the LEDs, I wouldn't think
a few coin cells would last that long. They're basically intended for
a load of a mA or so at best. You might do better with a 9V
"transistor" battery -- that's more along the lines of what's
considered a normal load for them. The 9V battery will also be cheaper
in the long run -- you can get a lot more power from one of these than
a couple of coin cells.

R1 is used to regulate LED current. The installation sheet suggests
120 ohms, 1/4 watt for a 5V supply. If you're using a 9V battery, you
should have a 270 ohm resistor (1/4 watt is acceptable, 1/2 watt is
preferred). If you've got a 12VDC supply, you should use a 390 ohm,
1/2 watt resistor. R2 (2 ea.) can be 10K, 1/4 watt for all values of
Vcc.

Now, most tilt switches are just normally open mechanical switches,
where either a metal ball or a blob of mercury will close a connection
if the device tilts. You can just connect the normally open switch
from the base to the emitter of the transistor for either of the
diagrams above. That way, when the tilt switch turns on, it will
prevent the transistor (and buzzer) from turning on. Simple. If your
tilt switch is normall closed (the contacts open when the device tilts)
you can either use it to interrupt the power supply to the LL sensor,
or interrupt the flow of current to the base of the transistor. That
works for either of the above diagrams, too. Again, simple.

to be disabled when someone's about to scald their lips. So, all we
have to do to complete this is determine what you're going to use as a
temperature sensor. Please post back and let us know what the teacher
suggests, or if you've already bought something.

I can say that sensing temp with a thermistor will require an EXACT
part number. Thermistor resistances are usually specified at room temp
(25C), and have an almost infinite number of different resistance value
vs. temp. graphs. If you have to use a thermistor, you will need to
make a current source to create a voltage across the thermistor
(usually just another transistor and a couple of resistors will
suffice), and an IC comparator to compare the voltage across the
thermistor with a contrived voltage which would represent overtemp. If
the thermistor voltage exceeds the setpoint, the comparator can turn on
and drive another small beeper directly.

As I said in an earlier post, it might be easier for a newbie to spring
for an LM34 IC, which works on 5V to 30VDC as a power supply, and
outputs 10mV per degree. You can then feed that voltage directly into
the comparator without worrying about thermistor curves. You may have
a bit of a problem in that the LM34 looks like a TO-92 transistor and
is not immersible (it will short out your power supply), so you might
have to glue the sensor to the bottom or outside of the cup. Actually,
you usually need to purchase special thermistors which are made with a
watertight sheath, allowing them to be immersed, too. Anyway, you need
to find this stuff out, and get back to us.

You're almost there. Get back to us with more information about
whether you've got an LL-type level sensor, and the type and specific
part number of the temp sensor you need.

Good luck
Chris

hi, just checking in over the weekend. I'm having a migraine now, so i
can't absorb a single thing Chris just posted. But, i will read it
again tommorrow. Just wanna tell ya all that, my name is Jean. -smiles-

OP = Original Poster, lol.. -slaps forehead- Now i know.. thanks John
Popelish for the heads up.

Jon, the tilt sensor is supposed to prevent the buzzer from going off
when the mug is in a tilted position. Which ever way is easier. But i
think it's either by, turning out the LLE and temp sensor when the mug
is tilted. or turning off the buzzer.

The tilt sensor was not specified. The LLE sensor was approved by my
teacher. He asked me to find a suitable sensor by using search engines.
Then i will print out the specifications of the component, and he will
decide whether or not it can be used.

I will read the all the post again tommorrow. And try to answer and
clarify all the fuzzy details. Thanks for bearing with me guys.

 

[Rich Grise]

Lastly, what is an OP? Does it refer to me? If it does.. I'm a her not a
he. -smiles-

Original Poster. So, do you have a name other than "obliquez"?

Thanks,
Rich