[MOVED] circuit related questions

[Venkadesh_M]

That was a maximum forward current LED series with 220ohm is enough..

 

[khangzing]

I know this,the voltage calculation should use 5v?no need to minus the voltage drop?and the 5/68 I get 73 mA..so should be ok right?but if connect the transistor it seem doesn't work...zzz...

 

[khangzing]

Why there is 0 A in base?i measur the voltage is about 300mV...zzz...with 0A it will in off state right...?

 

[Venkadesh_M]

Yeah always... The base base voltage must be above 650mv(0.65V) to turn on transistor, there shd be base current in mA...

 

[khangzing]

Te voltage is provided by micro controller right?if I connect the rc2 pin to base of transistor,the voltage is from microcontroller?and why only about 300 mV..

 

[Venkadesh_M]

If the microcontroller drives high there will be more than .65V it shows that the micro controller output is low or some low duty cycle output..

 

[khangzing]

Huh??how to make the transistor on?

 

[Venkadesh_M]

set the pin of microcontroller are if you want it easily connect the base resistor to V c c . . .

 

[khangzing]

I don't understand...set microcontroller pin are?i set portc=0x04
Trisc=0x00, correct?

 

[Venkadesh_M]

Exactly.............

 

[khangzing]

but still,i get 0A......zzz...

 

[Venkadesh_M]

what is the voltage at the MC pin?????

 

[khangzing]

nothing to worried about.....

first of all you have to learn a bit of pic programing...

try to make a led blink(in 1hz), after that reduce the delay and run in 38khz and now check with the oscilloscope..

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No need to attach bread boards, instead attach schematic of what you actually doing..

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the final programing part is very easy... and don worry about it..

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first try and complete the square wave.. after that convert it with ISR...

i think i understand the program above,is it like this?

sensor output connect to some port,then when the port is 0,count the time,but if i just want to do it for once,what can i do?because i want to know the time 1st only make it loop forever,for example i want to know for 1.5m,the ivalue, then set the ivalue to trigger the voice chip,you get what i mean?this post can found in this thread page 2.

 

[khangzing]

the voltage across ir emitter anode and cathode is keep on vary from 0.635v to 0.9v,how to increase it?by increase resistor value?
and the voltage on RC2 pin is vary from 1.6v to almost 0v.

now is working because the program transfer kit malfunction and i don't know it as we use in class few month ago. zzz...

 

[khangzing]

I'm getting the result but it only can detect not more than around 20-30cm,why.....?the current through ir emitter is 67mA and the voltage across emitter anode and cathode is 0.65-0.9v...is that the intensity of emitter not strong enough?

 

[Venkadesh_M]

Its enough and try to increase the frequency ON time, like more than 120ms...

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and congrats for your project... Thats why i told you to execute and check the kit with a small program..................

 

[khangzing]

i tried but i didn't notice that is the kit problems...because the "fake" square wave i got,i thought it is working... and why increase the frequency on time?no need to follow the datasheet?the operating voltages stated in the datasheet is 1.35v to 1.6v, but i only manage to get 0.635v-0.9v...

 

[Venkadesh_M]

That is bcs you are giving a square wave... when you are giving square wave it is called pulse width modulation or chopping

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the dc voltage will be as it is but due to continuously ON and OFF it will show a less Average voltage that is V*(Ton/(Ton+Toff)) That is called dutycycle

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You just getting the guidelines from the data sheet... Don change the 38khz frequency try to change the Timing of the 38khz present in the pin by that you can try a different distance..

 

[khangzing]

on for 200ms off for 300ms?

 

[Venkadesh_M]

yeah try lets see......