interfacing PC to an RC transmitter

[HSM1986]

hi every body , my name is hana and i need help to interface an RC transmitter circuit to the PC through LPT.
i tried the following method:
i removed the switches of the transmitter and replaced them with 2N2222 transistor where i connected the pin of the transmiiter IC "e.g back command pin" to the collector, and i connected the emitter to the ground of the circuit and LPT ,and finally i connected the base to D0 of the " LPT pin".
when i wrote the program for the interfaced circuit it worked well , when i send 5v to the transistor it provides an active low signal to the desired pin of the TX IC , and when i send 0v to the transistor it provides 1.44 v to the pin connected.
the problem is that the receiver doesn't respond to the TX after that interfacing.
but when i use the switches it works well.
sorry i know that i wrote to much details but i really need help so plz if anyone knows where i went wrong ?.
or a better way for interfacing? plz tell me, and don't hold ur information
waiting for ur answers and thanx in advance..
dally_nor2@yahoo.com

 

[colin mac]

You need a buffer in between the the parallel port and circuit. The parallel port can't provide much current and it's not clear what you've done without a schematic and knowing what current you're trying to give the base of the transistor.

 

[HSM1986]

but why do u think that the problem is in the current?and how do i know the typical current for the transistor?
the schematic of my circiut looks like the following:
**broken link removed**

 

[HSM1986]

sorry i forgot to say thanx for ur time colin

 

[colin mac]

It's not a good idea to drive a BJT from the parallel port because the port isn't good for sourcing current and could be damaged. If you want an inverter, a hex inverter
IC would be better. You need to attach the image to the post.

 

[ericgibbs]

It's not a good idea to drive a BJT from the parallel port because the port isn't good for sourcing current and could be damaged. If you want an inverter, a hex inverter
IC would be better. You need to attach the image to the post.

hi,
As Colin says you require an ic... the 74LS07 is an open collector non inverting buffer.

 

[HSM1986]

hi agian i'm sorry for asking alot,
but do u mean that i have to connect an inverter between the LPT pins and the TX pins?
and if that's what do u mean, do i need to connect two inverters to restore the original signal that i want it to drive the transistor???
can u answer me plz i realy need ur help....

 

[Mikebits]

hi agian i'm sorry for asking alot,
but do u mean that i have to connect an inverter between the LPT pins and the TX pins?
and if that's what do u mean, do i need to connect two inverters to restore the original signal that i want it to drive the transistor???
can u answer me plz i realy need ur help....

Just invert the bits in your software.

 

[HSM1986]

colin i realy tried to attach the pic ,but i didn't know how!!
although i think i gave a specific explainantion for the circuit and it's almost looks like the circuit in this website: **broken link removed**

 

[HSM1986]

ooh yes that's right thanx mike , colin and eric for ur help
i'll try what u told me guys and then will tell u the results, wish for all the happines.
c u soon

 

[Mikebits]

To post your image, instead of using the quick reply box, click post reply button, at the bottom of the screen is a button marked manage attachments. From there you can upload a pic from your PC.

 

[ericgibbs]

hi agian i'm sorry for asking alot,
but do u mean that i have to connect an inverter between the LPT pins and the TX pins?
and if that's what do u mean, do i need to connect two inverters to restore the original signal that i want it to drive the transistor???can u answer me plz i realy need ur help....

My earlier post:

the 74LS07 is an open collector non inverting buffer.

hi,
Why two invertors when a non inverting 74LS07 will do the job.?

 

[HSM1986]

hi guys, i tried what u told me last time i used 74S04 hexa inverting IC " coz i don't have the 7407 IC" and i connected the output pins "D0-D5" of the LPT to the inputs of the 7404 IC, but when i send 0 v via the LPT pins and measure the input of the 7404 IC i find that it is 1.56v , i don't know what's going on!! is the LPT damaged or something?
can anyone answer me plz

 

[ericgibbs]

hi guys, i tried what u told me last time i used 74S04 hexa inverting IC " coz i don't have the 7407 IC" and i connected the output pins "D0-D5" of the LPT to the inputs of the 7404 IC, but when i send 0 v via the LPT pins and measure the input of the 7404 IC i find that it is 1.56v , i don't know what's going on!! is the LPT damaged or something?
can anyone answer me plz

hi,
I would recommend you post a diagram showing how its connected to the Parallel port and which pins you are using on the 25way PC parallel port.

Which program are you using to drive the PC port.?

We need to see what you are doing...

 

[HSM1986]

ok eric the circuit schematic is in the file sent i hope it's clear so u can help me .....
and the programing language that i'm using is VB6 and the program is like the following:
out &h378,&h00
this command will be send when a command button1 is pressed
if command button2 is pressed the following command will be send via the LPT:
out &h378,&h00
note that i connected only one pin of the LPT..

 

[HSM1986]

where r u guys???
plz don't leave me unhelped

 

[ericgibbs]

where r u guys???
plz don't leave me unhelped

Hi,
Look at this dwg

Check the voltages I have marked on the drawing.

EDIT: are you using Windows XP Pro, if yes do you have the inpout32.dll in the Windows System directory.?

 

[HSM1986]

hi eric thanx for ur directions, i'll try to add those resistors and then will tell u what will happen.
and about the input32.dll, yes i have it in my directory..