Search results

Search Forums New Posts
  1. KrisBlueNZ

    logic probe

    Is the circuit now exactly the same as what I posted, apart from the 741s instead of the LM393? If so, and the LOW LED doesn't work, it's probably because of the input range of the 741. The LM393 is pretty widely available, I think. You really ought to get one.
  2. KrisBlueNZ

    logic probe

    No, the 741's input voltage range doesn't go close enough to the supply rails. Even the LM393 is getting close to its limit at 5V supply and past its limit at 3.3V supply. Yes, C1 is just for smoothing.
  3. KrisBlueNZ

    Project Help!!

    LTC1541/2 looks like a nice IC. Maximum supply voltage 12.6V is a bit close for my liking (absolute max is only 13V). Also not ex stock digikey or element14.
  4. KrisBlueNZ

    Project Help!!

    LM393 supply current is a bit high, typically 400 uA, maximum 1 mA or 2.5 mA at 30V supply. It's a lot lower than other standard devices though.
  5. KrisBlueNZ

    Project Help!!

    This version has a quiescent current below 0.2 mA.
  6. KrisBlueNZ

    Project Help!!

    Simplicity. A circuit with a comparator will need about the same number of resistors, perhaps one or two more, and a buffer transistor, so it's the choice between two transistors or an IC. The need for battery power changes things though. I would want less than 100 uA quiescent, which eliminates...
  7. KrisBlueNZ

    Project Help!!

    Cool :-) Battery power will work but both circuits have idle current, which will run the batteries down over a period of time. The first circuit has lower idle current than the second, although the second will only draw about one milliamp. Your choice of battery will also be affected by the...
  8. KrisBlueNZ

    Project Help!!

    Here's a better design with hysteresis, as I explained in the previous post. It uses three transistors but it will have a cleaner behaviour. I'm not sure whether you'll want to tackle this circuit, being a newbie to electonics, but you seem pretty smart and I'm sure you can do it if you give it...
  9. KrisBlueNZ

    How do I find the right transistor?

    Poetic, but not true. The laws of physics can put quite a damper on wild and crazy ideas. Have fun, but I strongly advise you to (a) not give up your day job, and (b) not seek or accept "investment" in your project from others.
  10. KrisBlueNZ

    logic probe

    Yes. No. U1A is just a comparator; it compares the voltage at its two inputs. The voltage at its non-inverting (+) input is set by the three-resistor voltage divider, and does not change when the probe is touched to some voltage. When the probe is touched to a logic HIGH voltage, U1A's...
  11. KrisBlueNZ

    Project Help!!

    OK, the sensor you're using is a "force sensing resistor". It behaves like a resistor whose value varies depending on the pressure applied. It can't drive a solenoid directly. Even with 10 kg pressure applied, its resistance is about 250 ohms, which does not allow enough current to operate a...
  12. KrisBlueNZ

    Boiling capacitor!

    Yes, I think the 2~6 MHz figure was a typo. The components specified for the 555 give a frequency of about 1.3 kHz. That page links to another page, http://home.comcast.net/~ddenhardt201263/desulfator/desulf.htm which has links to other pages and some testimonials. There are links to two...
  13. KrisBlueNZ

    How do I find the right transistor?

    Please re-read what I wrote in my previous post: I have no desire to steal your thunder; if you've invented something workable and useful, you deserve it. But I suspect you would save yourself a lot of time and effort, and end up with a better design, if you had more experienced eyes looking at...
  14. KrisBlueNZ

    Boiling capacitor!

    That's an interesting article. Deterioration of lead-acid batteries is caused by the deposition of crystallised lead sulphate on the plates, increasing the internal resistance of the battery and preventing current flow. The article says that it's possible to dissolve the lead sulphate back into...
  15. KrisBlueNZ

    logic probe

    Here's the same design with more sensible resistor values and an input protection resistor. The input resistance is 35 kilohms. The thresholds are the same as before. BTW I noticed you wanted green for H and red for L. Logic probes normally use the opposite convention.
  16. KrisBlueNZ

    NPN vs PNP

    That circuit is designed to only use a PNP transistor. You can see this from the fact that the arrow on the emitter points TOWARDS the base. An NPN has the arrow pointing AWAY from the base. NPN and PNP transistors are NOT interchangeable! A circuit that is designed for one type will NOT work...
  17. KrisBlueNZ

    3.5mm Headphone Jack LED?

    I'd say it would be possible. You'll get twice the power if you bridge the left and right channels by driving the left and right outputs in antiphase, with say a 1 kHz sinewave or squarewave, and connect a transformer primary between the two signals. Use a turns ratio of around 1:20 or so, using...
  18. KrisBlueNZ

    How do I find the right transistor?

    Mongrel Shark, I don't mean to sound nasty, but you really have got hold of the wrong end of the stick. The wrong end of two sticks, actually. First, there is very little demand for a complete list of all devices of any particular category from all manufacturers, and as a former professional...
  19. KrisBlueNZ

    logic probe

    Simple logic probe using LM393 Here's a simple logic probe using an LM393 dual comparator. R1 and R2 bias the probe to a voltage half way between the HIGH and LOW thresholds of the logic family that you're working with. In this design I've assumed thresholds of 2/3 VCC and 1/3 VCC so the probe...
  20. KrisBlueNZ

    logic probe

    Don't use TTL. They have a low input resistance that will upset the voltages you're trying to set up in your resistor chain. A simple way to do what you want is to use a dual comparator such as the LM393. When the input voltage is above the HIGH threhsold, one comparator activates and the red...
Top