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Posts posted by EdwardM

  1. Hi Dan

    doesn't sound too difficult, essentially it's just an alarm clock (4, 7 segment LED displays or LCD display plus some means of setting time and an alarm time). 

    Thereafter it's just a dimmer circuit, fired from fully off to fully on for a programmable time (another 2 switches).

    I'm sure there are many on this forum who could design one, maybe even me, if and when I get the time.

    Nor should it be horribly expensive! (Take a look at the 'giveaway' clocks available and imagine the cost of adding dimming....zilch + zilch =



  2. Hi

    don't know if it will help but I'd consider using 3 of the parallel port lines to clock 3, 4-bit serial/parallel converters, each of which would be attached to a motor driver chip.  This will leave you a minimum of 5 parallel port lines available for your obstacle circuit (which could also be serialised in the other direction). 

    The software requirements shouldn't be too onerous as the stepper motors require on/off times to be in the millisecond range whilst the parallel port is capable of considerably higher speeds.


    Actually, you only need one parallel port line for serial data if the serial/parallel devices are cascaded, together with one clock line.

  3. Hi u

    from what I understand, a magnetic sensor actually senses current, therefore if your closed loop circuit is driven by a voltage then it should be possible to detect that current using a combination of X, Y and Z coils to determine an exact position,  it depends also on how far away you expect to detect the wire, is it a few cm? or 30-40m?

    Hope that helps


    You could also try a Google search on magnetic sensors

  4. Hi Staigen

    don't think so...

    I shifted the input gradually from 2.5v to 5v and got a gradual change of output from 0v to 5v which was the original requirement, this led me to believe that my original equation might be correct.

    Do let us know why you think that it's not linear.

    As you rightly say, "when the input 2.5v the output saturate at 0v" It is a rail to rail opamp with a single supply of 5v so that's what I'd expect to happen.

    And, "When the input is 5volt, the output saturate at 5 volt" ... Yes, also.

    "And the scale between is not linear", please explain - there are no reactive components in the circuit which would cause this nonlinearity.

    Thanks for agreeing that the opamps I bought to prove the circuit seem to be excellent.


  5. Hi wk

    I now realize I was being a bit lazy about the circuit I described, I used an online opamp calculator to provide the starting values but they aren't quite correct.

    What I have done is obtained some AD8601 rail-rail single supply opamps and did a quick build using a 500K pot as the feedback element and a 50K pot to derive the reference. 

    The reference was set to about 4.75v and the feedback set (by eye) at about 1:1, and lo and behold it did work.

    Put in 2.5v and you get 0v out, put in 5v and you get 5v out.  Unfortunately, I don't have the time to produce a graph to prove that the transfer function is linear, however, it should be and I leave it others who may have the time to carry it forward.

    Best of Luck


  6. Hi Chaps

    R1 and R2 provide an offset voltage of about +2.5v (your minimum input), this means you need something more positive than that at the non-inverting input to make the output voltage rise above 0v. The value of all the resistors is almost immaterial provided that they maintain the same ratio.

    With a bit of good luck and a following wind, it ought to work.

    Best of Luck


    PS If you are interested in the theory behind this, I'd suggest you read chapter 4 of OP AMPS for EVERYONE it's freely available on the web.

  7. Hi wk

    with this sort of problem you have to start with the transfer function. In this case you are transferring an input of between 2.5 and 5v into an output of 0 to 5v and it should be linear, ie Vout = m*Vin+C. (The equation for a straight line).

    So m will equal the slope of the line (5-0)/(5-2.5) = 2 and C from the same formula = -5 after plugging-in the value of m.

    Vin            Vo=2*Vin -5

    2.5                  0
    3.0                  1
    3.5                  2
    4.0                  3
    4.5                  4
    5.0                  5

    You then need an Opamp circuit to achieve this transfer function: see attached .png

    It would be a good idea to use an Opamp designed for single supply, rail to rail use and values of R1 to R4 (to start experimenting) are 1K1, 1K, 9K, 10K.

    Hope I've got this right  ???

    Best of Luck



  8. Hi mettula

    Test for open circuit (which a capacitor should be) using high Ohms range, there may be an initial 'kick' of the meter display but it should become infinity.

    Test for short circuit, anything lower than infinity Ohms indicates leakage and the worst case being a short circuit (0 Ohms).

    Test for good: One way is to connect a battery or power supply to the capacitor via a high value resistor and at the same time measure the voltage across the capacitor.  From a knowledge of the supply voltage and resistance of the resistor you can make a reasonably accurate guess at the capacitors value using the voltage rise time formula for a capacitor.

    Hope that helps


  9. Thanks MP

    the conformal coating is a good idea and should enable the transition from prototype to 'production'.  The reason for posting this idea was mainly to pass on the results of a lot of frustration when designs didn't work, whether mine or someone elses'.  Many is the hour I've spent debugging a circuit only to find that I'd inadvertently joined  A to B instead of B to C and if you are not sure whether the design or wiring is correct then inevitably getting the thing working seems to take forever.

    So, if you can take one variable out of the equation - Life Gets Easier



  10. Hi

    For some years now I've used a simple way of protoyping on 0.1in perforated boards which usually guarantees first time working.  I simply make an outline of each IC and pin name used as well as power supply terminals in a drawing program and then print them on paper.  Each outline is then stuck down on the perforated board using paper glue.  It's then very easy to follow your circuit diagram to join up each node of the circuit and it's a very useful aid in debugging.

    My favourite program is Visio, I'm sure there are many others, where you set up a 0.1in printing grid for each drawing and just add IC's until the page is full, I then cut out shapes as necessary, using a scalpel,  and glue them to the perforated board.

    As an example, here's one I made much earlier.

    No doubt there are many using this idea, but so far I haven't met them




  11. Hi shiks

    Whilst I have no 'hands-on' experience of jammers, from what I've read, this is a big subject...

    Could anybody please elaborate how a jammer actually works?

    If you are talking of radio reception jamming, this means making the reception of radio signals unintelligible or impossible in a particular region.  At least two and many other ways to do this,

    1. Is to use the original transmission and retransmit with a time delay or several time delays with antennas beamed to the place you want to cover, making the reception tedious in the extreme.

    2. Is to use the transmission frequency and beam 'white noise' at much higher power than the original into the chosen region thus drowning out the original signal.

    Does it have a particular bandwidth of operaton or it jams all the frequencies in a particular region?

    It really depends on who/why the jamming is being done.  There may be very good reasons why only one or several stations are being jammed and that others may be allowed to be received.  So, it can be selective - If you wish to deny a region communications entirely then you would use several high power, broad spectrum jammers and antennas.  If you wish to obscure one station then a high power, restricted bandwidth transmitter would be appropriate.

    Does that help?

  12. Hi cynicmonster,

    First off, interesting handle. ;D

    I am  currently in the market for a 'scope

    Makes me assume you've not had one before - You have to ask, what do I need it for?

    If your interests are in (relatively) low frequency analogue/audio then almost anything modern will do.  If you do a lot of digital work, even at low frequency, then think of looking at a scope with 5 to 10 times better bandwidth than the highest frequency you normally work with.  Also, if mainly digital, then storage facilities can be extremely useful.  Unfortunately, at this stage, the options start to mushroom together with the price.

    Myself, I work mainly with digital circuits and some analogue - max frequency of crystal would be 20-40MHz and the working frequency about 25% of that.  I use a Fluke PM3082, 100MHz 2+2 channel with autoset, autocalibration and electronic cursors.  The only thing I miss is the lack of trace storage.

    I've also felt the need for more bench space and so have been tempted, for the next one and when income allows, to go for a black box approach with scope and logic inputs plugged into my current PC/laptop.

    Hope that helps

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