The reason I'm using a 555 is because I want a slight delay after I push the button. I.e. I don't want "push button => make number", I want "push button, let numbers run for a second, and then stop".
If you have other ideas for implementing this using some sort of a random, feel free to hint me.
-- Sincerely, | http://bos.hack.org/cv/ Rikard Bosnjakovic | Code chef - will cook for food ------------------------------------------------------------------------
I was thinking of making use of the noisy bounce in the switch. Depending on the amount of noise, the cap (before the 555) will be differenly charged for each time of a button press.
Atleast in (my) theory.
-- Sincerely, | http://bos.hack.org/cv/ Rikard Bosnjakovic | Code chef - will cook for food ------------------------------------------------------------------------
-- Voltage Controlled Oscillator. Change the tuning voltage and the output frequency changes.
What's a VCO?
-- Sincerely, |
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If you use my idea of blanking the 74LS47, then you will not see the number until you release the button. Chances are that you will inject a random number of clock pulses when you push the button, and you may or may not add one more clock pulse after you release the button. With your approach, if you use a high enough clock rate, it will look like a
8 until you release the button. To me, both produce virtually the same effect.
For me and in a hobby project, it would depend on what I had in my junque box, and I would try to avoid buying additional parts. In a more formal design, I might go for your more hygienic approach, depending on the criticality of the application. In an educational situation, I would suggest building and evaluating all "reasonable" possibilities, including testing for failure modes and operating margins. Sometimes, cheap and dirty is OK, and sometimes it can lead to disaster. Learning the difference is part of developing some engineering judgement.
Probably? How many microseconds? Are you seriously suggesting this is a problem? I am guessing that, in a casual design, it would be hard to find a switch that was sloppy enough and to drive the display that hard. I can see how you might force it to produce an easily visible flash if that was the desired effect, but my version of that circuit would be more complicated.
In this application, my judgement is that it does not matter, especially if you cannot see the count when the switch is closed and you cannot discern it counting when the switch is opened. You may decide differently.
Now you are being unnecessarily picky. I think it looks more like an
8 with weak segments. At least, that was how I viewed my rapidly changing 7-segment displays (admittedly with 0-9 or "random" digits, and not cycling through 1-6).I did write "virtually". Chacon a son gout.
-- Depending on the duration of the bounce and how hard he drives the display, he\'ll probably see a flash as the switch bounces on make. >Chances are that you will inject >a random number of clock pulses when you push the button, and you may >or may not add one more clock pulse after you release the button.
-- For anything I\'m involved in which isn\'t a real-time emergency or a rig which needs to be put together to solve a problem once, _right now_ , I won\'t do "quick and dirty". Especially on Usenet. This is seb, and newbies and novice querants need to be given stuff which will work, unconditionally. If it costs an extra 25 cents or even an extra dollar, so what?
-- I posted a solution and a schematic for you here: news:rbctj11i6lk4a13fpuiqgo9lglt7alm0fp@4ax.com and am disappointed that you haven\'t commented on it, one way or the other. Did you miss it, perhaps?
Point taken. I did not realise this.
I was, however, thinking to use a low frequency output for the 555, perhaps 10Hz or something. The frequency is something I'm going to try out on my breadboard, until I find a reasonable value that I can use.
I will - of course - try your version as well since for high freqs it will yield the same output. I just want some action on the display after I press the button ;)
-- Sincerely, | http://bos.hack.org/cv/ Rikard Bosnjakovic | Code chef - will cook for food ------------------------------------------------------------------------
Why did you leave the D! and D2 inputs open, instead of pulling them up (prefereably through a resistor) like you did with the UP clock input?
Why not hardwire the D input to the 74LS47 to ground instead of connecting it to the Q3 output of the 74LS192?
You're right. I won't bore you with the details of how I messed up converting to a fixed-pitch font.
-- This one.
-- You must have misread something. My latest post (the one that shows blanking and the elimination of the decode) shows them pulled up to Vcc. A resistor isn\'t needed for LS.
That link doesn't work in my newsreader.
I'm sure I missed it. What newsgroup did you post to?
-- Sincerely, | http://bos.hack.org/cv/ Rikard Bosnjakovic | Code chef - will cook for food ------------------------------------------------------------------------
I found the post. I must have read it the other time without thinking about it. Sorry.
Using a simulator, I built the schematic in your post but I didn't get it to work at all. I'm sure I've missed something about the 555, although I can't see I haven't connected according to your schematic.
The oscilloscope in the application shows 0V on the 555's output when the switch is open, and when I close the switch the scope reads 9V (i.e. VCC in my circuit). I do not see any pulses at all, except for when I open the switch again, then the scope drops to 0V and I have a nice square wave.
Here's my version of your circuit:
-- Sincerely, | http://bos.hack.org/cv/ Rikard Bosnjakovic | Code chef - will cook for food ------------------------------------------------------------------------
--- _______ _________ Yes, there's an error in my circuit. TRIGGER, (pin 2) not DISCHARGE (pin 7) should be connected to THRESHOLD, like this:
Vcc |S1 O | +-----[1K]----+ O | | +-------+ | | +--|TH OUT|--+-----|-----> To '192 DOWN clock | |__ _| | +-O|TR R|O-------+ | +-------+ | [0.1µF] 7555 [1K] | | GND GND
Sorry about that.
Also, reduce the 10k resistor from the RESET pin to ground to 1000 ohms. If you don't, you may find that the chip oscillates with the switch closed _or_ open!
If you're using a bipolar 555 instead of a CMOS 7555 and you have trouble getting it to oscillate using the above circuit, you may want to try the astable shown in figure 1B at:
-- John Fields Professional Circuit Designer
I am surprised that you did not actually build a circuit this simple. How do you learn about "practical" issues like layout, parasitics. contact bounce, etc?
I would have said that you confirmed that his simulation replicated your diagram accurately, and that you were the one who actually found the error. I would have given him credit for finding the error if he had said that he had a question based on reading the data sheet, and then asked you why you did it one way when he would have interpreted the data sheet differently.
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