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# walid

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## Posts posted by walid

1. ### TV's and monitors maintainance and repair Forum

i want a community (forum) like this electronic-lab community, where they discuss about  TV's and monitors maintainance and repair
thank you very much

2. ### SMP power supply

it is not difficult questions, i need answers ................ wait walid

3. ### BJT biasing formulas

good discussion

5. ### a low value wattage resistance

hi guru
we all know that resistors are used to limit current to some value
can a 0.5 ohm resistor limit current and to what level
secondly: why it so big 10 watt, what if i use a 0.5 watt regular resitors

no no, i'll ask my question another way:
what exactly i want to know that: what should i think when i see say 0.5 ohm 10 watt resistor in any board

power = I*I*R
10 watt = I*I*0.5
I max= 4.5amper
so i shoud expect that this R can safely pass a 4 A of current

is it true guru

thank u guru

6. ### a low value wattage resistance

hi
in many many circuits u faced a wattage resistance
for example in a PC monitor i see a 1 ohm 5 watt and in a low cost inverter in our project section you can see a 6 0.5 ohm 10 watt
also in many car batt charger you find one directly before the batt

why this resistance
can i replace it with a thick long wire
thanx
7. ### SMP power supply

Hi
In the Fig shown below is the input part of a switching mode ps
as most of us know the 220VAC is connected directly to the rectifer (4 diodes) through a filtering network
the rectifier o/p is about 310VDC
in some SMPS there is a one main filter capacitor 400v 220uF or so
in another there are two main filter capacitors 400v 220uF or so (C53 and C54 )in the sch below)
then this 310VDC is connected to the collector of Q16 and a snubars diode (damping diode)

My questions are:
1) Why using 2 caps (C53 and C54 ) instecd of only one
2) why using two transistors Q16 and 15 instead of one
3) if the voltage at the collector of Q16 is 310VDC what it should be at the Emitter of the same transistor
4) can u summarize the operation of this part of the circuit

thank u very much

8. ### What the meaning of .....

In fact you make it very clear thank u all very much

9. ### What the meaning of .....

What the meaning of hybrid
i read the following in the STR50330 datasheets:
Hybrid IC voltage regulator
thanx

10. ### Infrared Remote Control

thank you guru very much you really helped me

11. ### Infrared Remote Control

Hi guru

then experiment with different modulating frequencies to see if it is more sensitive to one.

are u mean the Tx freq?
OR u mean the Rx freq through R1 and C1, and if it respond to some freq what the output at pin 3 of the nand gate

thank you very much
12. ### Infrared Remote Control

Try to forget this MOD
I have one and its datasheet, i know its pins and wait your answer to costruct the circuits above

i want to get logic 1 or 0 or any thing else at pin 3 of the nand gate when someone pass, is this possibe or not, or you have a better idea

thanks

13. ### Infrared Remote Control

Hi guru

look at the two figs below,
If i use these circuits as Tx and Rx, and put my idenyified MOD....

that is if i put and aligned these two circuit

14. ### Infrared Remote Control

Hi guru

ok, lets agree that Radio Shack doesn't have the specs for the MOD anymore so nobody knows what it does.

i need you help in designing a gate guard using IR MOD as RX and IR diode as Tx
i baught  the RX mod's

i search the net but no circuit satisfied me

15. ### Infrared Remote Control

Hi

The MOD accepts a 40khz IR signal that is modulated at 4 khz. When a signal is received the MOD will go low. The sensitivity of the MOD is set by different values for R1 and C1.

from that I understand that the modulating sig is 4khz and the modulated (carrier) sig is 40khz

Look at the fig below:
the freq of the transmitter sig is calculated from:
f = 1/[0.693 x 0.05 uf x ( 2.2k + 2 x 1K)] =6.871kHz niether 40 nor 4 khz

R1*C1 = 0.4 sec

from where he had that values of freq

16. ### a very new Idea

Hi

my friend asked my help in his design
he wants some sensors placed some where in a gate that counts the visitors come in or out. when the number inside the room is say ten, the gate must closed and prevent more people from inteing

i tell him that he may use a controller like PIC16F84A and use two pair of IR TX and RX placed like to horizontal parallel lines one pair connected to say A1 port as i/p and the other pair to another i/p say A2
if a person cut ir connected to A1 then A2, then, this person is assumed to be entering the gate
if A2 then A1 he is out
the cotroller sums or substract till ten and close the gate for some period of tme

My questions:

(1) is this idea is the best for this progect or not?
(2) if it is OK can you help me in designing these sensors, the Tx is an IR diod connected to pin 3 of 555 IC. and the infrared receiver module .....

i need you help may be some links or any thing else
thanks

17. ### Transistor combinations questions

the two switches must not closed at the same time to avoid short circuit

18. ### Audioguru FM Tx

Hi guru

How to do this?
19. ### Audioguru FM Tx

hi guru

The battery voltage quickly drops to 7.2V

quickly =15, 30, 45, 60 .... hour!
20. ### fm

are u mean that the tapped coil acts as a step down auto transformer!

21. ### fm

hi

Some simple FM transmitters have the antenna connected to a tap on the coil. Then things getting near the antenna don't affect the tuned frequency as much.

Are u mean by "things getting near the antenna " my hands, and why when connected to the tap of the coil the osc be more stable
22. ### Tunning

Hi

Thanks Audioguru,

Since the topic is tunning(radio), I recently found an old audio/radio system for TV. The Volume control knob said :o motorized volume. I took it apart, and I think I saw motor. I'm not sure how this thing works? ???

the motor acts simply as your hand
i have a remote controlled cd, when i press the + or - volume i can see the volume nob rotate
it is connected by a motor rotate in two direction as the polarity applied on its terminals

For the Varactor diodes, i can add to what my big friend guru said that its capacitance is inversely propotional to the applied voltage; whev v high , c is low so the tunned freq is high

good luck
23. ### Transistor Question

yes it is very small like that

I'm pleasure, it is the first time i can help a friend in this great community

good luck truf

always I get all my project's parts from my old junk so i check them especially the transistors, you can say that i check more than 5000 transistors in that way and always the difference be that small.

24. ### Transistor Question

I understand his question in another way

may be he ask like this

if he has a transistor on the table and he wand to identify its terminals and type

use your digital multimeter diode function, first assume your trans is npn type, then put the red wire in one leg and the black on another leg .... repeat this untill you have a reading with the red on one lege and the black one time on the 2nd and then on the 3d
then the leg in contact with red is base and the others are C and E the bigger reading is E and the smaller is C

if u can't get any reading then assume it is pnp and repeat the above with the black first to one leg assumed base....

may be u hardly understand me but i want to help
thanks

25. ### Audioguru FM Tx

Hi guru

I HOPE U READ IT ALL

I understand u but i intend to use this inside a building of 4 floors, i want to talk while move from place to place, may be inside the lifter ........

when i first test it with that problem mentioned above my son talk near mic inside a room while i'm going away from the building, i hear him at about 150 meter and still hear the transmitter noise at more than 300 meter, there are many things in between.

I want to spend any time to succeed, but i'm afraid from that after spending this time and still have those problems of stability; its freq moves away
and the human body affect and the clearness of the received voice

In my work I have pair of wireless (about 200 meter) with LCD and 8 channels and some functions like outoscan..... i remove its cover to take a look, one second and i quickly close it, it contains many SMD ICs and tiny parts, i feel not OK, disappointed, in fact it is one of my big dreams to build one pair with one function TX and Rx voice with good fidelity and range.

Now  I ask u some questions:
1) you said the antenna must be about 80 cm long, is it important the diameter of this wire and if it have a plastic cover or not; that is can i use a 1.5 mm wire like that used in the electrical power connections

2) to reduce human body effect why not to enclose the oscillator stage inside a metal can like tunner used in TVs

thank you audioguru

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