| Electronics > Beginners |
| Discreet startup delay? |
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| KL27x:
What kind of micro is it? I'd maybe ponder letting the micro boot up, first, with a low speed internal oscillator and all I/O configured to draw next to nothing... Then have the micro switch the power to the other thing with a transistor. Then go about business. Maybe simply by letting the micro boot first by a millisecond or 10 might solve your problem without jumping thru any additional hoops? (I.e., maybe it's the initial "capacitance" draw of the micro when power is switched on that is causing the other chip to not power up successfully, rather than the quiescent current draw; e.g., try letting them take turns, micro first.) I'm sure you know it, already, but the ramp up of voltage has to be stiff enough and stable enough to get the oscillator in your other IC started... and the micro and it turning on at the same time can cause problems... which your micro would seemingly be handling better (most modern micros have some built in power-good hold/reset circuitry). For 555, google 555 + one shot and you will find schematics. The 555 comes in CMOS variant with a lower quiescent current than the originals. But honestly, it's dumb for this, because this doesn't need to be very precise. I'd use the LC circuit to bias a FET. Just reading the datasheet and wiring up the 555 and external components (whether by hand or in CAD) would take more time that it's worth. And it will have a startup draw of some magnitude, itself, on top of that quiescent draw. Maybe it is just as bad as the microcontroller. |
| spec:
--- Quote from: KL27x on November 24, 2018, 02:44:08 am ---For 555, google 555 + one shot and you will find schematics. The 555 comes in CMOS variant with a lower quiescent current than the originals. But honestly, it's dumb for this, because this doesn't need to be very precise. I'd use the LC circuit to bias a FET. Just reading the datasheet and wiring up the 555 and external components (whether by hand or in CAD) would take more time that it's worth. And it will have a startup draw of some magnitude, itself, on top of that quiescent draw. Maybe it is just as bad as the microcontroller. --- End quote --- Those are exactly the unsatisfactory 555 delay circuits I was talking about. The 555 is a great chip, but it has a couple of missing features that make it unsuitable for quite a few applications. That is why I would like to see the schematic. I think for pretty much any question you could reply with, "search the internet" :) "dumb" is a sweeping statement and meaningless "start-up draw" ? "Quiescent current" ? |
| Zero999:
--- Quote from: spec on November 24, 2018, 12:57:40 am --- --- Quote from: Hero999 on November 23, 2018, 11:20:27 am --- --- Quote from: spec on November 23, 2018, 06:42:08 am --- --- Quote from: rhb on November 23, 2018, 01:10:21 am ---Don't beat your head against a wall. Use a 555 and move on to the next problem. --- End quote --- Could you post a schematic. I have never been able to get a satisfactory startup delay circuit with a 555. --- End quote --- Post a schematic of what you've already tried and we might be able to suggest where you've gone wrong. --- End quote --- I have already asked rhb for a satisfactory 555 circuit, so I cannot see the purpose of your rather patronizing statement. If you posted a satisfactory circuit that would be a much more constructive way to illustrate where I have gone wrong. ??? --- End quote --- I apologise. I thought I was responding to the original poster. I didn't read it properly. I thought he'd already tried a 555 circuit and was having problems with it, but wouldn't post the schematic. :palm: Yes, a 555 circuit is one way to achieve a delayed power on, but I think it's a hack. I believe this relates to a different project with lots of things connected together and a current surge or grounding problem is most likely to blame. https://www.eevblog.com/forum/beginners/4-20ma-loop-powered-application/msg1961933/#msg1961933 |
| spec:
Thanks for the reply H99. :) I have tried many times to make a decent delay timer from a 555, but the only way to get the function is to use a differentiating capacitor from the supply line, and that is a complete no no for obvious reasons. I recon the simplest approach is to use an 74HC14 hex Schmidt, capacitor, resistor, and diode. First person to post the schematic gets the cigar. ;D |
| Zero999:
Why not simply configure the 555 timer as a Schmitt trigger? |
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