# Search results

1. ### [SOLVED] need help in figuring our the LED frequency

- so, the bigger the capacitance, the lower frequency the LED will work ?
2. ### [SOLVED] need help in figuring our the LED frequency

i am simply testing an LED to see what is the maximum frequency it could work with .. at 3MHZ.... the waveform looks like noise ....or similar to triangular wave... why does it happen ? - A resistor alone cannot do this, you would need an active current source and sink circuit --> what is the...
3. ### [SOLVED] need help in figuring our the LED frequency

can i get a circuit diagram where i can test an LED ? please... i need to figure out this.. - - - Updated - - - i got the voltage waveform across the LED... the DC offset is 5V from the frequency generator.. is this the right way to test a single LED ?
4. ### [SOLVED] need help in figuring our the LED frequency

so, i simply connected a LED (forward voltage of 3.3v) with a series resistor (85 ohm), that should give 20mA of current to the LED. - then , connected the frequency generator to the series circuit, the LED worked pretty good at about 900kHz .. but when i kept to 10Mhz or more than 3-4 Mhz...
5. ### [SOLVED] comparator maximum frequency help.............................

what is the maximum frequency that Lm239/339/239A comparator can operate on ????
6. ### relation between bps and frequency

for hyperterminal when i choose 9600 ... is it the baud rate or bps ??? if it is bps... what frequency it is ? 10kHz ?
7. ### relation between bps and frequency

If i sending 9600bps ..how to approximate what frequency it is ? - lets say if i am giving 10kHz square wave....--> what Bps it is ?for 10khz frequency how many bits i can send per second at max? - on the other thread i saw 1Hz is 2bits... so 10kHz is 20kbps ???
8. ### [SOLVED] LED/PHOTODIODE waveform

can you give me some material related to this so that i can study ?thank you :)
9. ### [SOLVED] LED/PHOTODIODE waveform

i gave 5v supply.. for 85ohm ,the LED is getting 20mA.. i want the function generator to drive LED directly..but is it possible to feed the function generator in the above circuit in the picture :) ??
10. ### [SOLVED] LED/PHOTODIODE waveform

i am newbie..can you explain me what u mean by observing forward current... so,if i keep a voltage supply to an LED,i cant keep a frequency generator ? - can you provide me a proper circuit to test an LED ?@20mA current - so that i can modulate LED and can see the output from LED in a...
11. ### [SOLVED] LED/PHOTODIODE waveform

hmm...maybe i should start from the beginning...how do i modulate a single LED properly...at what points i have to keep the connection of frequency generator >?might need a capacitor too
12. ### [SOLVED] LED/PHOTODIODE waveform

the waveform across the photodiode looks like a sawtooth...but how come when it is connected to op-amp the wave changes to square ? - i simply modulated an LED(connected to frequency generator 10khz)no matter what waveform i give,the shape across the photodiode is the same... for example..for...
13. ### [SOLVED] LED/PHOTODIODE waveform

I gave square across LED but the the photodiode diode detects sawtooth waveform.. which is clearly not a square wave,,why is that >??
14. ### [SOLVED] transistor gain calculation

so how will we know that 10 or 20 value is ok ? we can also take 40 for sure in this case right ?
15. ### [SOLVED] transistor gain calculation

I have seen a lot of calculations where they take GAIN as 10 or 20 instead of the original value in the datasheet.For example 2n2222 transistor VCC = 5 ,Led(Vf = 3v). For Ic = 20mA,Rc = [VCC-VF(LED)-VCE(SAT)]/Ic = [5-3-0.25]/20mA = 87 ohms. Ib=Ic/Gain = 20mA/110 = 0.18mA Rb = [Vcc-Vbe]/Ib =...
16. ### [SOLVED] basic current measurement value through LED

for high level is 48mA .... how to get for the low level ?
17. ### [SOLVED] basic current measurement value through LED

the current through LED is 48mA with DC offset of 5V...(LED forward voltage is 3.34V) - the top waveform is from frequency generator and the bottom one is from the LED-5v/div - )
18. ### [SOLVED] basic current measurement value through LED

why square r0ot 2 ? - information of freq generator : frequency - 10khz trig level - CONT DC offset - 5V LIN Pulse width variable - 10ns transit time - 7ns output attn(db) - 0 - anything i am missing ? - i checked the Vf for the white LED... it is showing 3.3v (with 100ohm resistor in...
19. ### [SOLVED] basic current measurement value through LED

RMS value of 3.53?? how do u cameup with 3.53????
20. ### [SOLVED] basic current measurement value through LED

i designed a basic circuit as in the picture.When i given the voltage from voltage regulator.The measured current through LED is same as the simulation = 12.7mA. but when i connected to the Frequency generator(10kHz with DC OFFSET of 5V), the current through the LED is double the value ??why is...