Simple Remote Question

[cl10Greg]

So I am into the basics of electronics and have a quick question. I want to make a simple remote using the 32KHz receiver that radio shack sells.

So basically it will be hooked up to a 555timer and wait for the transmission from the remote. My main question overall is on the remote. To get the remote and the receiver to work what exactly do I need?

From what I was thinking all I would need is an emitter and 32KHz crystal but I am sure that there is more to it then that. So can someone please fill me in on this?

 

[crutschow]

The IR receiver I found at Radio Shack is 38KHz, not 32KHz so you need to generate a 38KHz IR signal, if that's the device you have. You would need a crystal oscillator or microprocessor to generate the 38KHz signal. You would use this to drive a simple one transistor amp to drive one or more IR LEDs (more for longer range).

You could also use a standard remote control that operates at 38KHz. According to the reviews of the Radio Shack device, the Sharp remote and others operate at 38KHz but RCA/Phillips operate at 36KHz.

What is the purpose of the 555 timer?

 

[cl10Greg]

the idea of the 555 timer is to activate a pull solenoid to open a lock. I am sure there are better ways to do it but thats the rest way I can think of it. But now I think about it would that just make the solenoid unlock and relock instantly? lol I am not sure. Anymore input is greatly appreciated.

 

[crutschow]

the idea of the 555 timer is to activate a pull solenoid to open a lock. I am sure there are better ways to do it but thats the rest way I can think of it. But now I think about it would that just make the solenoid unlock and relock instantly? lol I am not sure.

Are you opening the lock so someone can go through a door? If so, just make the 555 time long enough to allow the person to open the door. I would think 5 seconds or so would suffice.

 

[cl10Greg]

Thank you very much

 

[cl10Greg]

One more question, any suggetions on the power source and transistor? I am thinking i was a good 5 to 10 foot range on this.

 

[crutschow]

One more question, any suggetions on the power source and transistor? I am thinking i was a good 5 to 10 foot range on this.

A 2N2222 NPN transistor will drive up to 800mA so it would be good enough to drive several high power IR LEDs such as the 100mA device from Radio Shack. Two or three of these diodes should give you a good 10 foot range. Even one might work if you wanted to experiment.

To calculate the required base current to turn the transistor on, use a beta (current gain) of about 10 to insure that the transistor is saturated.

When connecting more than one LED in parallel, each diode must have it's own current limit resistor (calculated to give about 100mA with whatever supply voltage you are using).

 

[cl10Greg]

Ok, I will give it a try and let ya know the results. Thank you again

 

[cl10Greg]

Update

Ok so I haven't did the parts yet but I am just check my math before I do to make sure I know what is going on. So here we go.....

I have attached the circuit that I am pretty sure will work. That is using the same IR diode and npn2222 transistor. So I have a single AA battery as the source with 400mAh battery life. The beta I am using is 10 to keep the NPN saturated.

First I want to calculate the Collector Current (IC). IC needs to be 100mA to run the diode so either I can use a resistor to limit the current to the diode or I can supply enough to the transistor to limit it down to 100mA (this is an assumption, is that correct?).

So according the equation β=IC/IB, 10 = 100mA/IB and thus IB need to be .1mA. So to make IB = .1 we need to use R=V/I. R = 1.5V/.1mA = 15K. So if R1 is a 15K resistor then the output of IC should be 100mA which would be enough to turn on the diode. Is that correct?

The other way I could see this being done is not regulate the 400mA coming in but you get 4A output according to my math. β=IC/IB, 10=IC/400ma, IC=4A. But as you said the max is 800mA output so would this just burn the NPN? If it didnt then it would just be making 4A going down to 100mA which would be using more transistors.

If I did it the first way though I could just wire the transistors in parallel right?

 

[audioguru]

An AA battery cell with a capacity of only 400mAh might be an old carbon-zinc type or an old Ni-Cad type. Modern AA alkaline and Ni-MH cells are 2500mAh.

IR LEDs are about 1.2V so yours might not work if your AA battery cell is a 1.2V Ni-Cad.

In your circuit the LED is not connected to the positive terminal of the battery so it won't do anything.

 

[crutschow]

I have attached the circuit that I am pretty sure will work. That is using the same IR diode and npn2222 transistor. So I have a single AA battery as the source with 400mAh battery life. The beta I am using is 10 to keep the NPN saturated.

First I want to calculate the Collector Current (IC). IC needs to be 100mA to run the diode so either I can use a resistor to limit the current to the diode or I can supply enough to the transistor to limit it down to 100mA (this is an assumption, is that correct?).

As Uncle $crooge noted one battery is marginal to power the LED. Even if it works when the battery is fresh, the LED output will drop significantly as the battery discharges. You should use two to get about 3V (or 2.4V if you have NiCds).

You can't reliably regulate the collector current in a transistor by controlling the base current since the beta can typically vary by a least a factor of 3 from transistor to transistor. It also varies with temperature. Thus you should use a resistor in series with the diode to determine the current.

 

[HarveyH42]

the idea of the 555 timer is to activate a pull solenoid to open a lock. I am sure there are better ways to do it but thats the rest way I can think of it. But now I think about it would that just make the solenoid unlock and relock instantly? lol I am not sure. Anymore input is greatly appreciated.

Wouldn't pretty much any TV remote unlock the door, since you are only detecting the center frequency? The receivers work, even if the center frequencies don't match. I've been off by almost 2kHz. Guess it's not too important, locks only keep honest people out...

 

[cl10Greg]

Wouldn't pretty much any TV remote unlock the door, since you are only detecting the center frequency? The receivers work, even if the center frequencies don't match. I've been off by almost 2kHz. Guess it's not too important, locks only keep honest people out...

Hah very true but speaking of which, where does the crystal fit into this circuit? I guess I just completely negated it haha. That is the last component I think that I need for the transmitter.

You can't reliably regulate the collector current in a transistor by controlling the base current since the beta can typically vary by a least a factor of 3 from transistor to transistor. It also varies with temperature. Thus you should use a resistor in series with the diode to determine the current.

So for this I can just run in diodes in parallel with the corrected picture all with there own current limiting resistor of course?

I will post the math and circuit for the receiver to verify that and see if I have any trouble.

Thanks for all the help so far also

 

[cl10Greg]

another question, would it be safer and more efficent to do an RF remote instead? How much of the circuit overall would have to be changed if i decided to go this route?

I bring this up because the fact that If i have this lock on the door I still need the IR reciever to be visibile on the outside of the door correct?

 

[mansir]

I really like the idea of a remote controlled door lock. Are you working from schematics on a website? If so, any chance you could link me to them?

 

[cl10Greg]

I really like the idea of a remote controlled door lock. Are you working from schematics on a website? If so, any chance you could link me to them?

No, I was just going off of theory and what i did learn in my electronics class that I can remember =).

So I have done some brief research RF as well and here is the jist of what I got out of it.

So according to most things I have read it sounds like that the RF needs a encoder at the transmitter and decoder at the receiver. They still have different band ranges (usually in the MHz from what I seen) but you need to have an antenna that can transmit. The ones I was looking at were roughly 3V/4.5mA to operate.

So I don't know what to do. The main thing I want to accomplish was unlocking the door but is this possible like I said with an IR (as in can it transmit through the door to unlock it)?

Please let me know on the IR and RF if you can.

 

[cl10Greg]

still not sure where the crystal goes in this circuit =(. Help please