assignment help

Discussion in 'Homework Help' started by alsar88, Nov 30, 2014.

  1. alsar88

    Thread Starter New Member

    Nov 30, 2014
    i have to design a circuit diagram for the following requirements:
    -power in 9Vdc, power out +/- 5 Vdc at 150 ma
    solution: im not sure yet, maybe use two op amps ?
    edit: im going to use two regualtors that take the 9Vpp input and turn it into a +/- 5Vdc output
    - power off after 5 minutes
    solution: have this part done using a 555 timer in monostable
    - gain channel 12Vp-p Vout = 0-3Vdc
    solution: so im thinking of using a rectifier then having a summation op amp with a potentiometer to vary from 0-3 volts.

    extra add ons--
    - an amp with vin 12 Vpp and vout 5Vpp adjustable
    - also how can i change the mono stable timer so when its dark, it decreases from 5 mins to 2 minutes
    Last edited: Nov 30, 2014
  2. alsar88

    Thread Starter New Member

    Nov 30, 2014
    i guess no one is welling to help, its ok :/ i guess........
    i have added a high side switch to the for the first part
    third part (gain channel i changed up completely, first design wasnt working. i turned toward a op amp which is working fine the way i set it up
  3. bertus


    Apr 5, 2008

    Post a schematic of what you have upto now.
    That way we can see where changes are needed.

  4. WBahn


    Mar 31, 2012
    So you post a problem at 10:47pm and then follow it with a post less than an hour later moaning because strangers that have lives and work and sleep aren't spending every minute just waiting for you to post a problem so that they can rush to your aid.

    Gee, feeling a bit entitled, aren't we?
  5. alsar88

    Thread Starter New Member

    Nov 30, 2014
    relax man, dont need to take to that heart like that.
  6. atferrari

    AAC Fanatic!

    Jan 6, 2004
    Just 3 posts and you feel entitled to complain? He is right.

    What you know about willing or not willing to help of people that you do not even heard of before?

    Too much from a newcomer and certainly not the best way to make anyone willing to help.

    You could have posted a schematics by now.
  7. shteii01

    AAC Fanatic!

    Feb 19, 2010
    I noticed that requirements changed from one line to the next. I don't waste my time on projects that don't have requirements.
  8. alsar88

    Thread Starter New Member

    Nov 30, 2014
    ouch you guys are not friendly at all. thanks for being such a welcoming comity. i didnt mean it to offend any of you and you didnt have to take it to the heart like that.
    and by the way, no change in requirement, just changed the way i approach i had for the problem.
    if its bothering any of you that much i would honestly just ignore this then because not a single person gave a slight suggestion or even commented on my approach solution to the problem.
  9. alsar88

    Thread Starter New Member

    Nov 30, 2014
    ill make a better copy of my drawings on paint and post it up. thanks for the suggestion. i have my general idea of the setup, just need to do the calculations as of now for the first three requirements.

  10. alsar88

    Thread Starter New Member

    Nov 30, 2014
    this is what i have done so far.
    - i have my regulator voltages working perfectly fine (i.e +/- 5 vout)
    -the timer for 5 minutes is working perfect as well but its useless right now since i have to change the resistor with a photo cell to account for change in light

    problems im facing:
    -placing a photocell at the first part parried with a 1k resistor gets the 5 min change time to 1 fine but i dont know how and why it works. so i think its wrong.

    in the works:
    -the instrumentation amp is still at work, i have a feeling it will work fine.
    -the capacitor tester, i started but hoping it will turn out right.

    i hope this covers all ground, sorry for the bad grammar, i have been up for god knows how long and i the temperature in this lab is like +30 C. im dying......
  11. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    After a brief look at your work it's not clear to me what you are trying to achieve.
    Forgetting about the design details it would be useful if you state in a few dot points what your goal is.
    What it the purpose of the timer?
    What is the purpose of the diff amp?
    What is the role of the photocell?
    What is the capacitor tester?
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    What is the overall project or assignment?

    So far, all I seen is a compilation of circuits with no clear purpose. An overall block diagram would be nice if possible.
  13. alsar88

    Thread Starter New Member

    Nov 30, 2014
    hello, sorry for the late replay. ill make a more clear schamatic after im done my exam tomorrow.
    this is an all purpose circuit.
    it has 3 mandatory parts that it has to include:
    -the circuit takes +9Vdc in and outputs + and - 5 Vdc (at 150ma)(this voltage is to be used for all purposes needed)
    soln: i used a linear regulator and a switching regulator to output these voltages

    -the circuit to shut off after 5 minutes
    soln: i used a monostable 555 timer at the input (+9Vin) that will shut down the circuit and can be retriggable with a switch

    -a gain channel with a 12Vpp and Vout 0-3 Vdc (this voltage is to be used for all purposes needed)
    soln: im using a difference(i believe thats the one i used) with a -5Vdc shift. the op amp will be powered with the -/+5 volts i have from the 2 regulators

    -using a cds photocell (light sensor) to decrease the 5 minutes time to 1 minutes when its dark. ill be using pin 5 on the 555 timer and set up a voltage divier with the cds photocell

    -capacitor tester
    2 soln:
    1) set up a mono stable circuit with a 55 timer and have the resistor as a constant and vary the capacitor, setup a data table for the time is takes to discharge for the standard values of the capacitance.
    2)using an astable to trigger a mono stable and measure the voltage of the varied capacitor using a DMM

    -an instrumentation amplifier with 12Vpp and 5Vpp output( it will have a gain adjustment) (this voltage is to be used for all purposes needed)

    I hope that is clear enough, please let me know if im not communicating something clearly. appropriate the help.