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Recent content by cct314

  1. C

    low quiescent current, 30v Vin, 5v out voltage reg?

    The FETs that I had in mind were P-channel rather than BS170's, which are N - a bit of a sticking point, perhaps. Only the "high side" 24 volt transistor would need to be P-type, but if you weren't worried too much about wasting a tiny bit of base current a PNP bipolar could be used, instead...
  2. C

    low quiescent current, 30v Vin, 5v out voltage reg?

    Do you have a tap point on your 24 volt battery at a lower voltage - say 12 or even 6 volts - to which you may attach the low-dropout regulator? If you are worried about unbalancing your battery bank, this may not be an issue: Some of the very low quiescent current regulators draw only a few...
  3. C

    Adjustable regulator modules

    Having used a number of those inexpensive Ebay switchers (w/out the metering) - some of which look exactly like the ones in the picture - I can say that they are certainly worth the price, which is less than that for which I can get the parts! I did build one of these into a device that runs...
  4. C

    Ferrite Bead

    For the purposes of suppression of ringing and VHF parasitics, I would presume that the 10 ohm resistor would provide the majority of effect. This might also reduce resonant/ringing if whatever is driving it (say, a transformer) has the tendency to do so when terminated with a highly...
  5. C

    Single AA Battery Low Detection

    From what I can tell from the data sheet, the PIC18F1220's 1.2 volt reference is not accessible to the user in any direct way - that is, it cannot be routed to an A/D input for a ratiometric reading. If one wants to read the output voltage of the converter, the LVDIN could be useful, but if the...
  6. C

    Single AA Battery Low Detection

    I had a problem like this on a (different) PIC where the supply was not well-regulated (it didn't need to be!) and I used a bandgap voltage reference diode - essentially a 1.2 volt Zener, although they come in different voltages and are well-behaved with respect to temperature. It was connected...
  7. C

    Resistor noise at RF frequencies?

    Were I curious about this I would: - Listen to the noise level with a 50 ohm resistor/dummy load across the receiver. Disable the AGC (or turn up the RF gain to effectively do so) and connect an AC voltmeter across the speaker if you want. - Now, repeat the above steps, connecting a 10k, then...
  8. C

    micro satellite transponder design

    I would recommend a bit of web research on your part. What you seem to be asking about is a "bent pipe" type of transponder - that is, a signal that is put into the input of the transponder is frequency-converted and amplified, appearing on the output at a different frequency. These do not...
  9. C

    Building a simple power strip with emi/rfi filter for treadmill

    If you have not already done so, I would "home run" your DSL connection to the NI (Network Interface) as this will go a long way toward making your DSL "immune" to what might be happening inside your house in terms of RFI/EMI. In short, there are two ways to connect DSL to modem: - Have it...
  10. C

    micro satellite transponder design

    Fundamental question: Do you want said transponder to be frequency-inverting or not?
  11. C

    30W LED driver - EMI concerns?

    If one wanted to go "all out" to make sure that such a device was "clean", this is one of those situations that can be "made" or "broken" by a board layout - and the components chosen. C1 and C7 should be of the low ESR types (electrolytic or monolithic ceramic) connected on the opposite side...
  12. C

    Help with AC & LEDs

    I believe that there are several problems happening here: - The operating voltage of your LEDs is very close to 12 volts. Blue/white LEDs like to be powered from 3.6-4.2 volts, but if you drop below that on a per-LED basis, they get very dim, very quickly: There's a very sharp voltage "knee"...
  13. C

    DIY a PIC Programmer

    Having used PICs since the very early 90's - and a lot of different PIC programmers - my "favorite" was the Picstart Plus, a serial port programmer. Alas, it is no longer actively supported and serial ports are getting hard to find. When replacing it I settled on the PicKit 3 (which is much...
  14. C

    Bare Piezo Transducers

    If the bare monomorph is held near the ear, or (better yet) pressed against a flat, somewhat flexible surface (thin metal, cardboard) even very low-level drive signals should be easily heard. Because these devices operate in a thickness-shear mode (I believe) the momentum of their change in...
  15. C

    Bare Piezo Transducers

    A monomorph (the disk portion of a ceramic transducer of which you speak) is excited largely by the dV/dT of the driving signal - that is, it being a capacitor, it is the sudden change in voltage across the device that will cause the most current to flow and the mechanical effect. An emitter...
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