URGENT HELP NEEDED

[mr. mister]

i want to feed the information output via the information line of a radio receiver into the pic (port RA0)
Also want to put in a crystal oscillator to generate 4MHz frequency.
I want to pass the output from port b to an infrared emitter diode,i know i need a transistor to amplify the current across the infrared emitting diode.
This is the circuit i have comeup with so far.

I don't know the input or output characteristics of the PIC16F84A.
Source into circuit is alsofrom the same channel from the radio receiver.

can someone tell me where i have gone wrong with my circuit? also where changes need to be made.

Thanks

forward current of IR emitter diode = 100mA

 

[Nigel Goodwin]

i want to feed the information output via the information line of a radio receiver into the pic (port RA0)
Also want to put in a crystal oscillator to generate 4MHz frequency.
I want to pass the output from port b to an infrared emitter diode,i know i need a transistor to amplify the current across the infrared emitting diode.
This is the circuit i have comeup with so far.

I don't know the input or output characteristics of the PIC16F84A.

It's all listed in the datasheet, but they are basically logic level inoputs and outputs, with an enhanced output current capability (20-30mA, if I remember correctly?).

If you don't already have the PIC, I would suggest you use a current device, rather than an old more expensive, lower spec, device - the 16F628 replaced the 84 years ago.

Source into circuit is alsofrom the same channel from the radio receiver.

If this from a radio control receiver?.

can someone tell me where i have gone wrong with my circuit? also where changes need to be made.

Looks OK to me! - I'm presuming you aren't showing the HT decoupling capacitors?.

What are you trying to do?.

 

[mr. mister]

firstly i am trying to get a current of 100mA flowing across the IR diode.

don'tknow what base current value to se for the transistor in the schematic. Don't know the resistance value either to use across the diode.

 

[Nigel Goodwin]

firstly i am trying to get a current of 100mA flowing across the IR diode.

It's not at all critical, and you work it out from ohms law, simply divide the voltage drop required across the resistor by the current (in amps) - so if we assume 3V across the resistor (rough assumption of 2 across LED and transistor) then 3/0.1 = 30 ohms. Either a 27 or 33 ohm would be close enough, and as I've assumed the LED and transistor drop on the low side, the current should be under 100mA.

don'tknow what base current value to se for the transistor in the schematic. Don't know the resistance value either to use across the diode.

You need sufficient current to turn the transistor hard on, something like a 470 ohm should be fine, or a 1K - again, it's not critical.