HT12E and HT12D remote control

[Joshff91]

Hi

I cant get the Data LED's, at the decoder, to respond to my input from the encoder, any ideas? thanks. Pictures underneath...

I have recently purchased a few HT12E and HT12D ICs. i made a remote circuit using - letslearnelectronics.blogspot.in/2012/07/introduction-to-encoding-and-decoding_1610.html?view=sidebar

I have also been using holtek data sheets
HT12E - holtek.com/pdf/consumer/2_12ev120.pdf
HT12D - holtek.com/pdf/consumer/2_12dv120.pdf

I can get the valid transmission (VT) LED to energise and de-energise using a switch @ the TE pin on the encoder side of the circuit, or i can get it to permanently energise by connecting the TE pin to ground (active low) - this works as expected from reading both data sheets. However i cannot get the four LED's which are connected to the decoders data line to respond to the input from the encoder. They are permanently on. I have looked at many versions of this circuit online and they all seem to be the same. They all reccomend using switches on the data input @ the encoder.

Like i said all 4 of my leds stay energised....

Any help would be great thanks

 

[House0Fwax]

One thing I noticed, your diagram for the HT12E does not match the breadboard layout. In the diagram you have 'TE' grounded. On the breadboard it is tied to 'D11'.

 

[Joshff91]

One thing I noticed, your diagram for the HT12E does not match the breadboard layout. In the diagram you have 'TE' grounded. On the breadboard it is tied to 'D11'.

It doesn't make a difference. If i tie it to ground the VT LED is constantly on as it is constantly transmitting, hence why i have put it through the switch. I was trying to get some sort of control..

 

[audioguru]

Like I said on the other website, the capacitors for the 5V regulator are not ceramic and are too far away so I think the regulator is oscillating.

 

[Joshff91]

Like I said on the other website, the capacitors for the 5V regulator are not ceramic and are too far away so I think the regulator is oscillating.

Im not sure if my comment posted on the other website...

My multimeter and oscilloscope show a 5 volt regulated pwr supply. If it was oscillating surely it wouldn't work or it would be intermittent?

 

[audioguru]

All datasheets for the 7805 regulator are spec'd with and show a 0.33uF input capacitor and a 0.1uF output capacitor. They are not electrolytic because electrolytic caps have too much inductance. Regulators are stable with capacitance at high frequencies, not inductance which is the opposite.
Your multimeter will not show high frequency oscillation and the capacitance of your scope' cable might stop oscillation.

 

[Joshff91]

All datasheets for the 7805 regulator are spec'd with and show a 0.33uF input capacitor and a 0.1uF output capacitor. They are not electrolytic because electrolytic caps have too much inductance. Regulators are stable with capacitance at high frequencies, not inductance which is the opposite.
Your multimeter will not show high frequency oscillation and the capacitance of your scope' cable might stop oscillation.

This is my regulator, so i will try this and hopefully you were right!

 

[Joshff91]

Audioguru,

It says to use ESR solid tantalum. I'm short on time for this project and was wondering if these would work?

maplin.co.uk/p/10f-35v-tantalum-bead-capacitor-ww60q
maplin.co.uk/p/047f-35v-tantalum-bead-capacitor-ww58n

I'm using a 9v battery pwrsup and couldn't find any to match that. Will these 35V ones still work? will they just be less efficient?
Would it be worth waiting for 9v or 5v ones?
I can't seem to fin any with a low ESR.?

Also are my capacitors, that i am using now, in the right place? if so i'll just swap when i get the new ones...

 

[audioguru]

You have a low dropout 5V regulator. It is completely different to a normal 7805 regulator because to achieve low dropout its series pass transistor is a PNP that has some voltage gain, instead of an NPN emitter-follower without any voltage gain used in a 7805 regulator. Because the PNP has voltage gain then a pretty big output capacitor is needed, and tantalum is spec'd because it has much lower inductance than an electrolytic.

National Semi (not the Taiwan copy-cat company) invented the LM2940 low dropout regulator a long time ago, and it has problems. It needs an expensive tantalum output capacitor and it needs a load current.
For all my 9V battery operated 5V regulators I use the National Semi (they have been purchased by Texas Instruments) LM2931 low dropout 5V regulator. It uses an inexpensive 100uF electrolytic output capacitor and does not have a minimum load current.

The input and output capacitors should be mounted VERY CLOSE to the pins of the regulator IC. Yours are too far away.

 

[House0Fwax]

From what I have seen of these two ICs, they have a wide operating voltage 2.4V~12V. So there is no need for a 5v regulator in your circuit.

 

[Joshff91]

From what I have seen of these two ICs, they have a wide operating voltage 2.4V~12V. So there is no need for a 5v regulator in your circuit.

it's not v stable without it....

 

[Joshff91]

You have a low dropout 5V regulator. It is completely different to a normal 7805 regulator because to achieve low dropout its series pass transistor is a PNP that has some voltage gain, instead of an NPN emitter-follower without any voltage gain used in a 7805 regulator. Because the PNP has voltage gain then a pretty big output capacitor is needed, and tantalum is spec'd because it has much lower inductance than an electrolytic.

National Semi (not the Taiwan copy-cat company) invented the LM2940 low dropout regulator a long time ago, and it has problems. It needs an expensive tantalum output capacitor and it needs a load current.
For all my 9V battery operated 5V regulators I use the National Semi (they have been purchased by Texas Instruments) LM2931 low dropout 5V regulator. It uses an inexpensive 100uF electrolytic output capacitor and does not have a minimum load current.

The input and output capacitors should be mounted VERY CLOSE to the pins of the regulator IC. Yours are too far away.

Audioguru, thank you for your help! the 7805 works perfect as you suggested. I do have one more question if you could please take the time?

Using the circuit I have attached, with the TE pin tied to ground as shown. - The four LEDs (data outputs) energise straight away and the valid transmission LED energises so I know it is working fine. I push any one of the four switches and the corresponding LED on the output de-energises. Say I wanted to use D8 (data output) to power a motor when I press D8 (data input) how could I achieve this?

In its current state if I tired this the motor would run constantly until I pressed D8 at this point it would stop. I want the motor to run when I press the button...

Does that make sense?

If there a way of reversing it or using a component that would not turn on until i removed the current?

Thanks again for your help

 

[audioguru]

You are using a 9V battery. Its voltage drops to 6V during its life but a 7805 voltage regulator does not regulate when its input voltage drops below about 7V. You should use a low dropout 5V regulator when you use a 9V battery.
The minimum output current from an output of the HT12D is only 1mA which is barely enough to dimly light an LED but you are shorting its outputs with much more than 1mA. An output goes high when a button for it is pressed so to turn on a motor then an output feeds a series 1k resistor to the base of an NPN transistor with its emitter at ground. The collector will go to ground when a corresponding button is pressed and can drive a motor that has its other wire at +5V or +9V. The LED and its current-limiting resistor must be disconnected from the output and instead connected to the emitter of a PNP emitter-follower with its collector connected to 0V that has its base directly driven from the output.

 

[Joshff91]

You are using a 9V battery. Its voltage drops to 6V during its life but a 7805 voltage regulator does not regulate when its input voltage drops below about 7V. You should use a low dropout 5V regulator when you use a 9V battery.
The minimum output current from an output of the HT12D is only 1mA which is barely enough to dimly light an LED but you are shorting its outputs with much more than 1mA. An output goes high when a button for it is pressed so to turn on a motor then an output feeds a series 1k resistor to the base of an NPN transistor with its emitter at ground. The collector will go to ground when a corresponding button is pressed and can drive a motor that has its other wire at +5V or +9V. The LED and its current-limiting resistor must be disconnected from the output and instead connected to the emitter of a PNP emitter-follower with its collector connected to 0V that has its base directly driven from the output.

Originally i was going to power the transistor from my output where the LEDs are, but as i said the output goes low when i press the button.

I am just trying to apply what you just said to this. Maybe im just missing something

Im not sure if i was clear before. The outputs go LOW when you press the data input switch. The LEDs energise when power is applied to the circuit...

 

[audioguru]

You can use a relay or a Mosfet if the motor draws a very high current. But then the little 9V battery will die very soon.

You said before the LEDs de-energize (turn off) when the button is pushed, now you say an output goes low (which will turn on an LED) when the button is pushed. Which way is it?

 

[Joshff91]

You can use a relay or a Mosfet if the motor draws a very high current. But then the little 9V battery will die very soon.

You said before the LEDs de-energize (turn off) when the button is pushed, now you say an output goes low (which will turn on an LED) when the button is pushed. Which way is it?

Sorry the LED turns off when i push the button. The relay will supply a separate 24volts for the motor.

 

[Joshff91]

The data sheet says this which made me think when the LEDs energise the output is high and when they de-energise the output at D8-D11 is low, though my knowledge of this system is limited and growing, again thanks for the help!

Im using this data sheet - http://robokitsworld.com/datasheets/HT12D.pdf

This is my one working as soon as i connect the power sup earth cable -

 

[audioguru]

Yes, the decoder outputs are low when the power supply is turned on which lights the LEDs.
When a button is pushed then an output goes high which turns off its LED.

 

[Joshff91]

Yes, the decoder outputs are low when the power supply is turned on which lights the LEDs.
When a button is pushed then an output goes high which turns off its LED.

As always you are a great help!

Currently I am using a 36'ish centimetre piece of wire for my antenna, which is working perfectly. But eventually I would like to replace it with something that is more durable. Do you know what parameters I would use if I wanted to by a ready made one like this? I'm sure it is in the data sheets I am just unsure of what to look for, thank again-

 

[audioguru]

The antennas on my FRS communicators are only 8cm (3") long because they work at about 750MHz. The antennas on my radio controlled model airplanes are only 2.5cm (1") long because they work at 2.4GHz.