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  1. darrins

    Ground a astable 555 at startup

    I have a circuit that uses a monostable 555 timer to control an astabable 555 timer; something like the first circuit in the following image My circuit works ok, but occasionally, I'm getting some strage behavior when I first apply power. Sometimes, when I turn on my power supply, the...
  2. darrins

    timing circuit to run N-times

    I have a simple circuit that uses a 555 timer to turn on a stepper motor for a certain amount of time. I'd like to connect the circuit to a rotary switch to make the circuit run 1, 2, 3....N times. What's the simplest way to do this? Thanks. Darrin
  3. darrins

    voltage divider for AC

    I hope this isn't a stupid question. I want to use voltage from AC to power a circuit, but at a reduced voltage level. I'm not sure exactly how much voltage I need, so I want to build a variable voltage divider with a resistor and potentiometer in series. Is this a reasonable approach and, if...
  4. darrins

    Stupid op-amp question

    I'm trying to amplify the voltage DIFFERENCE between two inputs. One input (V2) is a reference voltage of about 1 volt. The other input (V1) is from a heat sensor that is fairly linear at 0.1 volt per degree Fahrenheit. So, for my application, the input from the heat sensor is about 0.7 volt...
  5. darrins

    Where to find LCD/LED displays

    Anyone know where to find low-cost LCD or LED numeric displays? I have a project that will display temperature in Fahrenheit, so I need a display capable of 4 digits. Thanks. Darrin
  6. darrins

    Iron-on PCB's w/ photo paper

    I want to try my hand at making homemade PCB's. I read an article describing how this can be done by printing the layout on glossy photo paper (w/ a laser printer) and then using an iron to transfer the toner to the copper clad PCB. The board is then etched w/ Ferric Chloride. Here's the...
  7. darrins

    Differential amplifier question

    I have a couple of basic questions related to a differential amplifiers. If these types of questions are better suited to the Theory Articles board, please let me know. :) I want to amplify the voltage difference between a sensor (Vs) and a reference voltage (Vref). I only want to amplify...
  8. darrins

    PWM using 555 timer

    I read several datasheets and application notes on 555 timers, but I can't seem to find the information I'm looking for. Specifically, I'd like to use the 555 as a pulse width modulator by using the control voltage (pin 5). The datasheets indicate that in monostable mode, the output pulse...
  9. darrins

    Mini golf cart from UPS batteries

    At work the other day, we smelled something burning in our server room. The culprit -- an old uninterruptible power supply (UPS). It's more cost effective for us to just throw these things away and buy new ones than try to repair the faulty unit. One man's trash is another man's treasure, so...
  10. darrins

    On/Off heater controller using triac

    In a previous post, I asked about designing a controller to regulate the temperature of a small tank of water. Ante suggested using a triac to control power sent to the heating element. After some reading, I also agree that this is a good technique; however, I haven't been able to find any...
  11. darrins

    Electronic weighing system

    I'm working on an appliance that dispenses a powder from a hopper using a feed screw. I want to control the dispensed quantity by measuring the weight loss of the hopper. This change in weight will be on the order of 7 grams to 40 grams. I figure that this could be done by either: a) using a...
  12. darrins

    source for strain gauges

    Anyone know where I can buy cheap metal foil strain gauges? I'm trying to make a "poor man's" load cell. Thanks. Darrin
  13. darrins

    Voltage req to heat small amt of water

    Any water heating experts here? I have a flexible heating element that is wrapped around an aluminum cylinder that contains water. It contains about 12 oz of water at room temperature. I want to heat the water to around 100 degrees Fahrenheit from an initial temperature of about 74 degrees...
  14. darrins

    HELP! 555 timer to control pump

    I am new to electronics, so I apologize for my ignorance. I working on a project that involves emptying a small tank of water using a solenoid valve. The valve is opened for a certain amount of time by using a 555 timer and a reed relay. When this timer goes low, the valve is closed, and...
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