ryeeson

Hello, The transistor will detect if there is a current flow through the LED right? so if there is a current, then the +5V will be the output at the transistor right? Thanks...

Thanks again Audioguru, I have Email you for another question. I still remember you said

The data sheet can be found with the link bellow. http://www.datasheetcatalog.com/datasheets_pdf/L/M/3/9/LM3915.shtml bassiclly i understand the LM3915 basic operation about what is the LM3915 does. What i dont understand is, how does the voltage/current flowing out to the LM3915's pin as shown in the diagram bellow..

i have this idea. Can i connect the signal to a ADC converter? let say i connect it to a PIC's ADC pin. we run the program to check the level of the converted signal.

how if i operate the LM3915 in bar mode? is there is any method else then you have mention above?

how about comparator? we can use comparator to compare 2 current right? comparator such as LM393 has a very low bias current. http://www.onsemi.com/pub/Collateral/LM393-D.PDF if logic not possible,do you have any suggestion?

CMOS Logic is new to me. I haven't have any experiance with it. Now i'm reading about it. okey. now the question arise, which Cmos logic to use? i never uses any before. What is the model number?

Hello Again. I come up with a new question. I'm planing to connect the 14th or13th (or 12th) LED to trigger the interrupt on my PIC16F84. I think that we can generate needed voltage for interrupt by connecting the signal form an LED to an logic gate. Here i use an AND

Hello, The circuit work very well using the Average detector. figure bellow show how i supply my Rhi. When i change the R1 to smaller value (20k), the first 2 LED will lights. When i use 220k, the first 5th LED wont light up (dot mode). It starting on the 6th LED. Playing with the R1 value can give me a good result without knowing what is the true Voltage or current for the Rhi. Any comment about the diagram above? how i can supply my Rhi with 1.6v? btw, the capacitor seem does not affect The Rhi? am i right? How do i make the LED to discharged slowlly? i meant, the LED suppose to light up quickly(sensitive) but light off slowlly? increase the C8 value will do the job?

Hello, i cannot figure out how the average detector work. It seem kind of half wave rectifier to me? well i'll try this out today. What value of the Rhi should I set? 2.5v?

every ( inverted signal)circuit need dual supply? is this what do you mean? do you mean integrator Op-amp? hemm this mean i need another circuit for integrator?

Hello, Can i use any average detector instead of the one in data sheet? I have some LM358. can i use them to build average detector for my LM3915?

you mean. i dont need transistor Q1,Q2 and Q3? so the output signal from pin7 should connect to my average detector? the rectified signal should connect to signal input on pin 5 of LM3915 right? then i'll update you soon. thankx

my bad.. i dint check the LM and LF datasheet :'( ok thanks for the advice. btw can i just replace your peak detector shown in the figure bellow(link) with the average detector? or do have some suggestion?

hello again, i cannot see the dual supply for the data sheet. Where am i suppose to connect the negative supply? How to change the led lights so that it lights not too fast and light off not to fast also?

Hello again. I've reduce the circuit gain by reducing the value of R5. And i'm happy with it. There is something i want to come up with after changing the R5 to a lower value (eg. 40k) there is no LED light up on the beginning (no sound). When I talk, the LED will lights accordingly but the problem is even if I talk Softly, the 10th LED will light. When I stop talking, all the LED is off. Another problem is the LED lights very fast. How can we make it have a little delay? So that we can catch our eyes on the LED display level? When I change the R5 to a very low value, the circuit cannot pick up any signal. How to make the LED less sensitive without sacrifice its 'true gain' so that the next LED Is harder to lights. Example, for normal library environment we set (guess) the 1st to 3rd LED is lights up (due to the air conditional unit noise) and this Level stay until someone makes a sound (talking etc) Which causes the 4th (to 5th...etc according to the sound level) to light up. Now the display level is seem not more then 30dB. That why I’m thought of cascading The LM3915. Or... it may be because your circuit is using the average detector shown bellow. May be I just need to change the peak detector to the average detector? (As shown in Picture 2?) But your peak detector seem don’t match with the one in the data sheet. peak detector average

u mean, to reduce the sensitivity i can choose wheter to reduce the gain or to increace the voltage at pin 6. i'll try again and update with you later. thanks.

Hello Audioguru, i've tried your project but i use the MC33171. sorry but i can't figure out where is your modified average detector. i've been work hard to understand your design. There is some question i would like to confirm with u. 1. When we do circuit analysis considering in DC signal, we don't include the capacitor(so inductor) in our analysis. The inductor become open circuit and the capacitor become short circuit. Am i correct? in the 1stage, you used an non-inverting op-amp. why we need the voltage divider? and what is the point of R3 connecting to the ground? You said that, "With low-level sounds, R15 in series with the resistor ladder at pin 6 creates 0.5V at pin 6. Therefore an input signal of only 0.5V lights the 10th LED. 15.8mV lights the 1st LED." my question is, 1.what happen if with high-level sound? so if with a low-level signal, there is no current from Q3 to R14? which will connect the 5v through R15 to pin 6(LM3915)? but that should provide pin 6 with 5v instead of 0.5 as you have mention. i need to alter the Rhi so that the 10th LED will light up if the input signal is high enough(i mean if the sound level is loud considering inside the library). i've check the output signal with an oscilloscope. The signal is something unusual for me. If i take reading form output on pin 7 of the opAmp(take your circuit as a reference), the signal seem have been half wave rectified. I've built a circuit exactly with your and take the band pass filter that you have suggest. The circuit works well but it's sensitivity is too much for me. When i talk softly, the 10th LED already light Up. (i operate it on dot mode). the sound-level around me never lights the first 3 LEDs. its always lights the 5th to 10th LED. How can i alter this? Can i alter this by changing the R15? may be i get it wrong.. the sensitivity is okay. But what i want to to is to control the LED. Let say i want the 10th led only lights if i the sound level is high enough example someone talk too loud or if i talk softly, the 3rd and 4th LED light up. or probably i just cascade the LM3915 but seem it wont work. I really appreciates your help.

Thank you very much for the valuable advice :) i use the average detector (from the LM3915 datasheet) before the signal to LM3915. :)

my project objecitive is to detect a noise in the library. this subject to noise caused when people(library user) talk louder. All those noise from low frequency is not a problem since it wont 'disturb' user. i want to filter a frequency from 0 to 1000 Hz.

Can i use this circuit in my project? but i dont need the very low sound. There is two thing i can do. 1st, i can add a high pass filter to the signal before the lm3915 input. 2nd, i can modify the circuit. in my opinion by changing the value of the R10(from 100k to 10k) will cut the low signal since the current have less resistance to the ground compare to the R8. am i correct? or by changing the R15 as you have mantion? With this 2 option, which one would u prefer/suggest? i cannot see how the Q3 act as a peak detector. again, i dont need the peak detector. i need average detector. How should i modify it?

Automatic gain control huh.. amazing theoryticly, changing the capasitor from 10v to a bigger(let say 50v) would slow down the charging process. What acctuly happend if i use 50v capasitor instead of 10v?

3. The R16 is a power resistor? Since mine is not powered by batteries, i dont need the Voltage regulator. am i right? you have mantion that this circuit has additional range about 20db. i dont get it! what range are they?

Thanx.. 1.What does the singal Rhi do? 2.Why use voltage regulatro since the supplied power is DC? 3. The R16 is a power resistor? 4. you forget to list the transistor :)

Thanks for the help. :) Can i use MC33171 instead of MC33172 without any modification to the circuit? Thanks in Advance.