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Posts posted by bonanz

  1. Hello,

    I have a problem with a dj mixer.  There is a decay on the crossfader. for a scratch dj the cut in time on the crossfader is very important.  My particular mixer seems to have a problem with a rc time constant most likely that causes a slight muddy sound when doing fast and complicated scratch moves.  It is hard to notice alone, but when compared side by side with another (top of the line) dj mixer, the difference in the 'cleanliness' of the cuts is evident.

    I'd like to graphically display the difference between the two.  I'd like to play a tone and use the crossfader to cut the sound in and out and compare the voltage, or volume level to inspect the slope of the decay.  This would probably be straight forward with a scope and measuring the voltage somewhere in the crossfader circuit, but I want to compare the two, but I am not willing to disassemble the 'top of the line' mixer I want to compare the faulty mixer to.  The faulty mixer I am willing to take apart, but I want to be clear that the problem is occurring.

    Can anyone offer any suggestions on how to creat a graph from the audio how quickly it goes from full volume to 0.

    here is an mp3 file of me playing a tone and cutting the sound with the crossfader


    click on the link, then click free at the bottom, then it will make you wait for approx 15 secs or so and then offer the link for download.

  2. Okay i've done some playing around with this circuit and i cannot get it to work for my application. I'm not worried about switching terminals because i am not using it as a typical dmm i'm using it to display a voltage in a circuit that will always be positive. I am using the LM2907 frequency to voltage converter and have it convigured so that the output voltage is linearly proportional to the input frequency (ie 200mv ~ 200hz) the max freqency i'd measure would be about 1200Hz which would correspond to 1.2v work perfectly on the 2v scale and i would just leave the decimal points unconnected. I have hooked up the project circuit, and did a test on a voltage divider to see if it was measuring correctly and it did measure the voltage, but i only had to connect terminal one to the voltage point and did not connect terminal 2 to anything and the voltage displayed correctly. (this is btw with the negative supply grounded). The LM2907 freq to voltage converter circuit i have completely working and outputing the corresponding voltage when i use a regular multimeter, but i would like to integrate this circuit with it to have a permanent display. any help would be appreciated.


  3. This circuit came up at the perfect time! couldnt have asked for a more perfect design for what i need right now, only problem is i don't have a -5 volt supply.  What would happen if i grounded that pin rather than using -5.  would that simply not allow for negative voltages to be measured? because i only need positive for my application. or is there a simple way to make a negative supply from only a +5 being available?



    Project Link: http://www.electronics-lab.com/projects/test/001/index.html

  4. Hello all,

    i want to display the speed of a model train, the optical sensors (link below) are placed around the track, and i am using the lm2907 to pick up a frequency off of them and change it to a voltage. then i was feeding that voltage into some cascaded LM3914 bargraph drivers to display the speed on 20 led's.

    I got the freq input going and had the LED's rigged up before, but now when i try to integrate them the resulting display on the row of LED's is really noisy and there seems to be a huge burst of voltage at low speeds, like if the train is going slow, whenever it trips a sensor the voltage leaps and lights almost all 20 led's for a split second and then drops back down. Just overall the response of the LED's seems too sensitive to fluctuations in speed, when i measure the output votage with a DMM and fluctuate the speed, the output voltage seems to increase/decrease appropriately without any wild fluctuations.

    So my question is how can i get the LED's to not be so sensitive it seems and read the voltage more like the voltmeter. Or can someone suggest another method to display the speed. Could i use a ICL7107 and a 3.5 digit display with a voltage divider to display the speed in like inches/sec or something. Would the ICL7107 have the same sensitivity problem? I guess i could probably also use an analog voltmeter and "redraw" the tick marks on the meter, but i'd like to have a nifty digital output of sorts. (note: i tried analog meter and similar results slightly better though, but still not good enough)

    The max freq i anticipate is about 30Hz maybe 40. so i want to display speed from stop to about 30 Hz. here is a schematic of the circuit.

    sensors being used


  5. Hello all,

    I'm having a problem figuring out how to go about achieving my desired results for my train's braking system. If a ttl level signal goes high i need to shut the power off to the Linear induction motor coils. These coils may have up to about 1A running to them to drive the train. The amount of current to the coils is controlled by a potentiometer. This potentiometer also has an optional switch so that when the pot is turned all the way down it makes an open circuit between 2 connectors, and once you strart to increase the resistance the switch closes (all separate from the actual pot prongs, but controlled by the pot going to 0). so okay here it is... i want to cutoff the power going to the coils when a digital signal goes high, and for the power to stay off until the pot has been turned all the way to zero opening the switch on the pot. then when the pot is moved up and the switch closes sort of "resetting" the pot. but once its back on, if that same signal goes high again cutoff the current to the coils and wait for teh pot to be "reset."

    Sorry if my description is a little confusing, i drew up a quick little thing to try to help visualize it. and remember the coils will be handling pretty high current (1A) so i'm thinking some type of small power transistor inline to the coils being controlled by the switch, some logic, and shutoff signal.



  6. I know this is something simple but i've done a little searching and can't find what i'm looking for and i can't work it up form scratch for the life of me....

    I'm looking for digital logic circuit/gate that everything starts at 0 (low) and then if high is input, the output is high, but only for about 5 seconds, then the output goes low again, nomatter if the input stays high or goes low again.

    I hope i explained it clearly, but basically the idea would be, press a button to turn on a LED or something for 5 seconds or so, if you hold the button down it goes for 5 seconds and turns off, if you press it and let go it will hold it for 5 seconds and turn off, either way once the led goes low it is ready to be turned on again.

    Thanks in advance guys

  7. Hello all,
    I am working on a model scale maglev train. along the track there are sensors that detect the positino of the vehicle and power current through a respective coil to form a LIM. I wanted to find an easy way to monitor the speed of the train by using the sensor frequency (evenly spaced) and to give an output. I am not real fond of microcontrollers so i planned to use an LM2917/LM2907 frequency to voltage converter, and then use that voltage to drive a row of led's using a LM3914. The only thing i didnt take into consideration is the train with respect to sensor position (about 4 inches apart) will be outputting a frequency at maximum of 1Hz which would not produce barely any voltage at all coming out of the FTV and therefore not drive the led's. I was wondering if someone was familiar with a way of multiplying such a low frequency into something that the FTV converter would find useful to put out a reasonable voltage, or possibly a simple, yet entirely different approach.

    btw. love this site, plan on hanging a round a lot

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