Hello,
Before stating my questions I like to give some background info first:
I am interested in modelrailroad circuits and I found this one from http://users.skynet.be/pro-rail/ukindex.htm:
The circuit is actually a variable current source for memory wire, with adjustment via the pot. The current is limited between 180 and 240 mA.
I tried to understand how the circuit works. I can calculate the resistance of 9.2 to 6.4 Ohms when the pot is turned at the emitter side. But I can not get to the values of 180-240mA.
So my first questions are (I tried several other forums for an explanation, but it seems that no one can really explain it to me.):
- Can someone explain me how to obtain the values of 180-240mA?
- What is the reason using the 4.7kOhm resistor?
Anyway, I still would like to use the circuit (even when I can't understand it), and control it with a pic16f628, hence circuit activated/deactivated.
Here my question concerns the connection from the pic port to the transistor (b-gate):
- Can I hook-up the output port of the pic to the transistor directly (including the 120 Ohm and 4.7kOhm resistors)? or
- Do I need a special resistor instead of the 120 Ohm/4.7kOhm)? or
- Do I need a second transistor stage between pic and this circuit?
- What to do with this 2.4V?
Any help concerning the theory of the circuit and a possible circuitry for the link to the pic is appreciated.
Thanks,
Guido
Before stating my questions I like to give some background info first:
I am interested in modelrailroad circuits and I found this one from http://users.skynet.be/pro-rail/ukindex.htm:
The circuit is actually a variable current source for memory wire, with adjustment via the pot. The current is limited between 180 and 240 mA.
I tried to understand how the circuit works. I can calculate the resistance of 9.2 to 6.4 Ohms when the pot is turned at the emitter side. But I can not get to the values of 180-240mA.
So my first questions are (I tried several other forums for an explanation, but it seems that no one can really explain it to me.):
- Can someone explain me how to obtain the values of 180-240mA?
- What is the reason using the 4.7kOhm resistor?
Anyway, I still would like to use the circuit (even when I can't understand it), and control it with a pic16f628, hence circuit activated/deactivated.
Here my question concerns the connection from the pic port to the transistor (b-gate):
- Can I hook-up the output port of the pic to the transistor directly (including the 120 Ohm and 4.7kOhm resistors)? or
- Do I need a special resistor instead of the 120 Ohm/4.7kOhm)? or
- Do I need a second transistor stage between pic and this circuit?
- What to do with this 2.4V?
Any help concerning the theory of the circuit and a possible circuitry for the link to the pic is appreciated.
Thanks,
Guido