Using remote control to turn on a motor

Thread Starter

Kelvin Lee

Joined Oct 22, 2018
111
Dear Sir/Madam,

I am new to this forum, not sure whether it is the right thread I posted here.

I want to use a home used remote control to turn on a motor to demonstrate the remote concept in class.

I have my own circuit design


I have several questions:
  1. When I use a multimeter to measure the voltage drop across the resistor and LED, it around -0.096V if no IR signal and 1.49V if IR signal. Do I use the wrong model of the transistor?
  2. Am I correct to place the LED at collector side of the transistor?
  3. Do I need to add a transistor between IR and base of the transistor?
  4. The output voltage is enough to light up a LED but not enough to a 3V motor if I replace a motor with the 150 ohms resistor and LED, should I increase the input power or replace with another model of the transistor?
  5. Is there any better circuit design to do the same project?
I would appreciate if anyone could teach and advise.

Best regards,

Kelvin.
 

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MaxHeadRoom

Joined Jul 18, 2013
22,387
Drawn a little unconventional, the power rail is normally drawn at the top of the circuit.
Also earth ground symbols used.
If this is for teaching, it is good to use proper conventions.
You may be better off with a Mosfet.
Max.
 

Thread Starter

Kelvin Lee

Joined Oct 22, 2018
111
Dear MaxHeadRoom,

Thanks for your advise, I will keep it in mind.

Except replacing the transistor with a Mosfet, is there any other need to be change such as the amount of voltage?

Do you mind recommend which part number of Mosfet I should choose?

What is the main problem I use the 2N4403? I am now familiar with the transistor.


Best regards,

Kelvin
 

MaxHeadRoom

Joined Jul 18, 2013
22,387
If a 3v motor, 5v would be ideal to overcome any impedance of switching components etc.
What is the current of the motor?
Do you have details of the detecting sensor?
Max.
 

danadak

Joined Mar 10, 2018
4,057
  1. When I use a multimeter to measure the voltage drop across the resistor and LED, it around -0.096V if no IR signal and 1.49V if IR signal. Do I use the wrong model of the transistor?
  2. Am I correct to place the LED at collector side of the transistor?
  3. Do I need to add a transistor between IR and base of the transistor?
  4. The output voltage is enough to light up a LED but not enough to a 3V motor if I replace a motor with the 150 ohms resistor and LED, should I increase the input power or replace with another model of the transistor?
  5. Is there any better circuit design to do the same project?
1) When bipolar switch transistor is on, saturated, its typically .3 - .6 V collector
to emitter. LEDs when on here are typical drops -



And of course the R drops some V. Sum of those 3 drops = supply rail = 3.3 in your case.

2) Thats correct, normally you would.

3) Depends on what output structure of IR receiver circuit is. Probably yes
I would say w/o knowing what part you are going to use.

4) As MaxHeadRoom points out MOSFET a good solution because it can get very close
to an ideal switch, means no loss in switch itselt if low Rdson. In a 3V system use a
logic level FET to do this, Vishay has some parts with very low turn on threshold (Vth
or Vgth).

5) Something like this -



MOSFET selection - https://www.vishay.com/mosfets/n-channel/gteq-5-lteq-20-v/


Regards, Dana.
 
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Thread Starter

Kelvin Lee

Joined Oct 22, 2018
111
If a 3v motor, 5v would be ideal to overcome any impedance of switching components etc.
What is the current of the motor?
Do you have details of the detecting sensor?
Max.
Dear MaxHeadRoom,

Thanks for your advice. In fact, I am a newbie to electronic, this experience is just demoing how an IR receive signal and then trigger another action, after that, I will use an Arduino to receive the signal and do some decision. Pure electronic is just a show case.

I get a motor and test with a multimeter, the current is around 140mA when 3V input. I have no idea the current need for the IR, should I need to add a resistor to it when using 5V power source? How much of resistance need? I only know the IR is labelled 1838.
 

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Thread Starter

Kelvin Lee

Joined Oct 22, 2018
111
1) When bipolar switch transistor is on, saturated, its typically .3 - .6 V collector
to emitter. LEDs when on here are typical drops -

And of course the R drops some V. Sum of those 3 drops = supply rail = 3.3 in your case.

3) Depends on what output structure of IR receiver circuit is. Probably yes
I would say w/o knowing what part you are going to use.

Regards, Dana.
Dear Dana,

Thanks for your reply. I may be too green and don't know how to read the datasheet, may I know how I can get the same information about
"typically .3 - .6 V collector to emitter."?

I don't know how I can know output structure of IR receiver circuit is. If need resistor, how much of resistance need?

Best regards,

Kelvin.
 

Thread Starter

Kelvin Lee

Joined Oct 22, 2018
111
Drawn a little unconventional, the power rail is normally drawn at the top of the circuit.
Also earth ground symbols used.
If this is for teaching, it is good to use proper conventions.
You may be better off with a Mosfet.
Max.
Dear MaxHeadRoom,

Could you teach me how I should draw this circuit?

Kelvin
 

ebp

Joined Feb 8, 2018
2,332
The 2N4403 should be quite satisfactory for the LED. It would be marginal if the LED were white, but for red, green or yellow it will be fine. (This is because a white LED requires about 3 V to light and you only have 3.3 V to start with, so any voltage drop across the transistor becomes quite significant.)

The IR receiver will be putting out serial digital data, so the LED will only turn on when the output is LOW. This means that the voltages you measure with a meter will be averages as the LED is being turned on and off at a speed far too high to see. A very small motor would probably be OK with this, but it would run at a reduced speed. You would need to add a circuit to "stretch" the pulses to keep the transistor turned on.

You probably should have a resistor of 1k or so in series with the base of the transistor to limit the current.
 

danadak

Joined Mar 10, 2018
4,057
Thanks for your reply. I may be too green and don't know how to read the datasheet, may I know how I can get the same information about
"typically .3 - .6 V collector to emitter."?

I don't know how I can know output structure of IR receiver circuit is. If need resistor, how much of resistance need?
For output V, Vsat spec, transistor hard on, look at datasheet for part. For a
MOSFET it is Rdson spec, and you calc V from ohms law, you know th Iload
and Rdson, you then know the V drop on output.

IR Receiver datasheet will give you, typically, what input and output looks like
from a functional point of view with rough circuit. Whats the part number you
are going to use. ?

Regards, Dana.
 

Thread Starter

Kelvin Lee

Joined Oct 22, 2018
111
IR Receiver datasheet will give you, typically, what input and output looks like
from a functional point of view with rough circuit. Whats the part number you
are going to use. ?
Dear Dana,
I found the label on IR receiver is 1838.

When I read the datasheet from https://cdn.instructables.com/ORIG/FT3/GKNT/IIQC8H9T/FT3GKNTIIQC8H9T.pdf, the diagram makes me very confused, I may not familiar with reading the datasheet. There are two pin diagrams in the datasheet. One shows the GND in the middle and another one shows the GND at the side. Do I misunderstand something?

Best regards,

Kelvin
 

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Thread Starter

Kelvin Lee

Joined Oct 22, 2018
111
The circuit in Post #5 should work, if using an Arduino then it could switch a Logic (5v) level Mosfet directly.
The 2n7000 is good for up to 200ma.
Max.
Thanks, MaxHeadRoom. May I know whether PNP is the only type transistor I can use in my case? Can it work with NPN?
 

danadak

Joined Mar 10, 2018
4,057
The application circuit in the datasheet is not the pinout, use the package
drawing in the datasheet which calls out GND as middle pin.

The datasheet shows the output with a NPN to GND and a R to its Vcc
inside part. So if you used PNP to switch load, yes you would put an
R between IR output and base of PNP. But there is no spec in datasheet
as to what limitations are for the sensor NPN current.

If you use NPN external you can, if datasheet spec more complete, use internal
R to limit NPN base current. Problem is spec sheet sloppy and does not tell
you what that value is. The only way you could possibly tell is measure the
output pin to Vcc resistance. But even that not reliable because spec sheets
over simplify in their block diagrams what's actually going on. You need
~ external NPN load current / 10 for base current to make sure it is in saturation.

All these reasons leads one to use a MOSFET rather than a bipolar to
insure you get a good switch behavior independent of output loading because
the sensor output is basically unloaded and will (should) give predictable I/0 levels.


Regards, Dana.
 
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ebp

Joined Feb 8, 2018
2,332
The receiver appears to be a copy of the Vishay (originally Telefunken) TSOP1838 which is obsolete. A datasheet which isn't awful can be found at
https://4donline.ihs.com/images/VipMasterIC/IC/VSMI/VSMIS06817/VSMIS06817-1.pdf
(url is from Avnet). The original was intended for 5 V operation but the copy appears to be OK down to 2.7 V. Since the datasheet for the copy comes from what appears to be a hobbyist vendor and kind of looks like it too is a copy (no manufacturer shown), the minimum supply voltage may be dubious.

The pinout is as shown in the package drawing. It is very common to rearrange pins for schematic symbols to make the schematic easier to read (compare symbols used for LM317 and LM7805 - symbols are quite similar but pinouts are very different). Pin names must be used to make symbols readable and pin numbers are commonly used for parts with more than 3 or 4 pins. Some devices have different pinouts in different packages, so care is required. Note the circuit in the Vishay datasheet shows pin numbers.
 

danadak

Joined Mar 10, 2018
4,057
With the datasheet ebp just posted the drive levels from sensor so poor you
basically have to use a MOSFET or Darlington, former preferred.

Regards, Dana.
 
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ebp

Joined Feb 8, 2018
2,332
If you want to drive a motor from the receiver output you must use a pulse stretcher otherwise no matter whether you use a MOSFET or a BJT you will be unlikely to get more than about half of the load supply voltage "into" the load. For clean drive to the load you will need additional active circuitry. For a low-performance stretcher, a carefully chosen logic level P-channel MOSFET could be used. A capacitor directly (or with just a small resistance between) across the output and ground of the receiver would be discharged much faster than it would recharge through the weak passive pullup in the receiver, effectively "stretching" the LOW time. The turn-on and turn-off of the FET would be "slow" (milliseconds to tens of milliseconds), but that would never be noticed with a motor. A FET is much more suitable in this case because the gate requires essentially zero current so it doesn't influence the time it would take to charge or discharge the capacitor. Using a P-channel FET means you can't use a motor supply voltage greater than the receiver supply voltage with the simple stretcher.
 

Thread Starter

Kelvin Lee

Joined Oct 22, 2018
111
The main difference with NPN/PNP in a circuit such as in Post #1 is just the polarity of the supply.
Max.
Thanks, MaxHeadRoom,

Yes, I read a lot about NPN/PNP circuit from Intenet, most of them like to use the attached sample circuit to explain the difference between two. It is very clear to show how the wring to the switch, but I have no idea how I wire the IR sensor with 3 pins, of course, the Vcc and GND from IR sensor must be connected to the circuit's Vcc and GND, how do I know where another side of the signal pin when I connect the signal pin to the base of the transistor? I think it is the most common question to most newbie user.

Best regards,

Kelvin
 

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