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  1. hevans1944

    4060 counter not accurate?

    I almost forgot... an inexpensive and very accurate (long term) timing source is the mains frequency. This is corrected by the utility every day to ensure the total number of cycles per day is always the same, meaning line-synchronized clocks do not gain or lose time. You can start with a...
  2. hevans1944

    Schottky rectifier

    Steve, I didn't see anything on the datasheet I uploaded that indicated the 1N5819HW is a silicon carbide Schottky diode. Are you sure that it is? The maximum operating temperature of 125 C is way below the typical maximum temperature for silicon carbide devices, and the plastic (rather than...
  3. hevans1944

    4060 counter not accurate?

    Pinpoint accuracy is a relative term. Typical accuracy of an RC timer with off-the-shelf components can vary quite widely and is usually temperature and voltage sensitive, depending on component selection and how the RC charge/discharge switching levels are determined. Probably the most accurate...
  4. hevans1944

    Schottky rectifier

    I am pretty sure a low-voltage 100 μF SMD capacitor is available somewhere. Try this link for starters. For the Schottky diode, try a 1N5819HW. See attached data sheet
  5. hevans1944

    Analog to Digital Signal Block Diagram Confirmation

    Well, actually, it would convert a 4 to 20 mA current signal to a 1 to 5 VDC input to the ADC. This "wastes" one fifth of the ADC conversion range. Unless there is a strong reason to use the 4 to 20 mA current loop (long distance between sensor and ADC input being a valid reason) it is better to...
  6. hevans1944

    Can someone please explain how step down. transformers work

    It has been awhile since I last visited the link provided by @davenn but, having looked again, I must agree it is an excellent explanation of transformer operation. Part 1 will generally provide all the information you need to specify and use any power transformer. If you want more details...
  7. hevans1944

    What is your favourite type of component?

    Indeed! Especially if you integrate a few hundred of them onto a single integrated circuit substrate! This revolutionized analog circuit design somewhere around the middle of the 20th Century. NMOS and PMOS (and later, CMOS) played catch-up for only a few years before soaring ahead to become THE...
  8. hevans1944

    Schottky rectifier

    The main (and maybe only) advantage of Schottky diodes, AFAIK, is their really fast recovery when reverse biased. Since there is no PN junction, per se, there are no charges (minority carriers in a PN junction) to clear out when transitioning from forward conduction to reverse blocking, leaving...
  9. hevans1944

    Schottky rectifier

    The "static" resistance, or equivalent series resistance Rs, comes from the Agilent datasheet, linked by the OP, for their SPICE model. The model has Rs in series with Rd which is in parallel with the forward-biased junction capacitance. Rs in their SPICE model is specified to be 6 Ω. More...
  10. hevans1944

    Schottky rectifier

    It would be most helpful if you would post the simulation parameters and the model used for each of these diodes. The static resistance of the HSMS-2822 is a relatively HUGE 6Ω and the typical dynamic resistance is an even larger 12Ω. This may help explain the simulated charging behavior when...
  11. hevans1944

    Sanyo Clock radio repair

    You need to use some common sense and a bit of creativity here. Perhaps a hypodermic syringe and a longish blunt needle will allow you apply contact cleaner more precisely. Again, a little bit goes a long way. I think we are done here. Thanks @davenn for the nice photo of the linear potentiometer.
  12. hevans1944

    What is your favourite type of component?

    I like these, too. An almost essential component when interfacing to "real world" analog signals for subsequent digital processing. Works well as a digital inverter if you don't need the Schmitt trigger functionality, often saving board space and obviating the need for another package. Note...
  13. hevans1944

    Specify "shunt resistance" for current measurement

    The "best" resistance value is the smallest value that will produce a measurable signal on your oscilloscope. Try using 0.1 ohms (or less) and set the vertical deflection sensitivity to 5 mv/div or less (if available). That will give you a "sensitivity" of 50 mA/div. If that isn't enough...
  14. hevans1944

    Low powered digital DC supplies?

    Sounds like a homebrew project to me! If the voltages will be "applied to plates inside an instrument in our lab," will there be any significant current drawn in the steady state? How about during switching (changing) voltages? How fast must the potential applied to a given plate settle to its...
  15. hevans1944

    Buffered High Speed ADC for embedded oscilloscope

    Fast sampling oscilloscopes with deep memory are pricey. For a USB device, check out this manufacturer. Not cheap, but less costly than a comparable bench 'scope from Tektronix, Agilent, or Rohde & Schwarz. USB bandwidth is not generally a consideration. Accquisition occurs in the box and...
  16. hevans1944

    Simple Switch using Photo Diode

    The link that @(*steve*) provided shows how to do what you want using three different light sensors: photo-sensitive resistor (typically a CdS cell), photo-transistor, and photo-diode. A cadmium sulfide (CdS) photo-sensitive resistor is simple, inexpensive, and may be more appropriate than...
  17. hevans1944

    Sanyo Clock radio repair

    I would try spraying some contact cleaner into the front slot using the small plastic tube that can usually be afixed to the push-button spray head. Move the slider back and forth while spraying and try to get the tip of the spray tube as far inside the slot as possible. Don't get too carried...
  18. hevans1944

    What is your favourite type of component?

    I like new, high-tech, components that I can get as free samples by visiting the manufacturer's web site. Sometimes these are only available as itsy bitsy teeny weenie SMDs, so it is problematical whether or not I can actually "play" with them. For example, I received an assortment of...
  19. hevans1944

    Trying to fix broken backlight on a Soniq E55V13A TV

    Sounds like there is at least one open LED in each array. Are the LEDs individually accessible for probing? If so, you can try putting a jumper across each one in turn (shorting that particular LED) until that string lights up. Remove the short and replace that LED. Of course this method of...
  20. hevans1944

    Question for BNC terminator.

    Absolutely! I forgot to mention that, maybe because I don't remember how you can distinguish between the two types if you don't have a VNA (Vector Network Analyzer) to measure them.
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