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Unread postAuthor: jackssmirkingrevenge » Tue Mar 05, 2013 4:30 pm

I hadn't seen the video in your previous post, great job!
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Unread postAuthor: mark.f » Tue Mar 05, 2013 4:46 pm

That control box is giving me fits right now. :P I had a diode in place to prevent the 555 from sinking current but I went to replace it with a better one and wound up installing it backwards ( :oops: ). Have to replace the 555 and diode.

The PWM circuit is for something completely unrelated though... hopefully I can put both on a cannon sometime in the near future.
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Unread postAuthor: dewey-1 » Tue Mar 05, 2013 6:07 pm

Mark;
Post a schematic or a link of the schematic you used.
There are shematics out there which are not ideal for the application.
Some even have gross mistakes.
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Unread postAuthor: mark.f » Wed Mar 06, 2013 12:39 am

Here's what I plan on using... it's used to heat a small coil, so switching frequency isn't terribly important.
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Unread postAuthor: dewey-1 » Wed Mar 06, 2013 9:02 am

There appears to be an error on the potentiometer wiring.
I will do a schematic for 5-95% duty cycle.
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Unread postAuthor: POLAND_SPUD » Wed Mar 06, 2013 10:28 am

That control box is giving me fits right now. I had a diode in place to prevent the 555 from sinking current but I went to replace it with a better one and wound up installing it backwards. Have to replace the 555 and diode.
You people still use 555timers ?

You can get an attiny45 for 1$

considering the price of the parts, extra components and time it is much cheaper to use a uC
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Unread postAuthor: mark.f » Wed Mar 06, 2013 10:47 am

dewey-1 wrote:There appears to be an error on the potentiometer wiring.
I will do a schematic for 5-95% duty cycle.


The potentiometer's wired as a rheostat so doesn't function as a voltage divider but a variable resistor... using only one pin and the center one (wiper). Measuring the one I plan to use gives around 50 to 1000 ohms... probably need a 10kohm one or larger though.

EDIT: PS, I bought a handful (25) of 555's from Mouser the last order I made for about $0.45 a piece... considering I have bags of resistors/ceramic capacitors and several "donor" circuit boards lying around, I'd have to say it's much cheaper to use a 555 to do something as simple as flashing an LED (what it's used for on that board I was referring to in your quote.) :P
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Unread postAuthor: dewey-1 » Wed Mar 06, 2013 11:01 am

[quote="POLAND_SPUD
You people still use 555timers?
You can get an attiny45 for 1$
considering the price of the parts, extra components and time it is much cheaper to use a uC[/quote]

Not necessarily!
What about the price of the programming interface or the parts to build one.
(Granted it is a one time investment.)

Someone may need a simple circuit without the need/desire to learn programming.

Mark, here is typical PWM 555 circuit.
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Unread postAuthor: mark.f » Wed Mar 06, 2013 11:53 am

I guess I have to actually study the workings of the 555 a little more to get why you would use a potentiometer to supply a fraction of the supply voltage to the trigger than threshold pins... I think either circuit would work but yours has the advantage of a constant switching frequency? Off to the books, lol.

EDIT: For instance, this makes more sense to me.
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Unread postAuthor: POLAND_SPUD » Wed Mar 06, 2013 12:42 pm

EDIT: PS, I bought a handful (25) of 555's from Mouser the last order I made for about $0.45 a piece... considering I have bags of resistors/ceramic capacitors and several "donor" circuit boards lying around, I'd have to say it's much cheaper to use a 555 to do something as simple as flashing an LED (what it's used for on that board I was referring to in your quote.)
I know 555timers are even cheaper but they are limited.

so it's like buying a pen for 0.5$ when you can an entire set comprising of a few pens, pencils, pencil crayons, pencil sharpeners, rulers, erasers etc for 1$
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Unread postAuthor: mark.f » Wed Mar 06, 2013 1:23 pm

Yes, but do you need a calligraphy set to sign a check? :D

If it makes you feel any better I am still looking at getting a PIC emulator/programmer along with an arduino and some ATiny's sometime in the near future... for instance, handling the problem of increasing duty cycle with a 555 PWM generator to respond to something like voltage drop on a battery during operation quickly becomes a headache.
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Unread postAuthor: POLAND_SPUD » Wed Mar 06, 2013 2:04 pm

for instance, handling the problem of increasing duty cycle with a 555 PWM generator to respond to something like voltage drop on a battery during operation quickly becomes a headache
that's pretty much the point - 555timers are cool but there are better ways to do stuff and it just happens that they are actually cheaper

ohh BTW just got a Launchpad board (well actually two one is for a friend of mine). just 4.30$ a piece (inlcuding shipping)

here is a simple example sketch sending temperature readings through serial
[youtube]http://www.youtube.com/watch?v=heCrsbBJxcg[/youtube]

Note that they can be programmed using Energia IDE
more on it here >>>
http://www.instructables.com/id/Use-Ard ... ad-MSP430/
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Unread postAuthor: dewey-1 » Wed Mar 06, 2013 2:05 pm

Many moons ago, about 1974, I designed a circuit based on a 555 and also 7555 which was used for 1 to 30 second interval timer.
It functioned but had poor repeatabily and was very prone to external noise causing false triggering. This is inheritantly due to negative edge triggering.
Try an electric drill in close proximity to the circuit and turn the drill on and off.
Poland Spud do this same test with your uC to see how noise immune your micro controller is. Let me know your results.

At that time I totally redesigned the circuit using a XR2240 and later a XR2242 and XR2243.
These all used positive edge triggering and had internal 8 bit or more binary counters. Problems gone after using something like this;
http://www.intersil.com/content/dam/Int ... fn2866.pdf

Actually I do not like the 555 for the above reasons. I discovered a lot of faults in using the 555's back then.

edit: XR (Exar) not ICM (Intersil) 72 series
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Unread postAuthor: POLAND_SPUD » Wed Mar 06, 2013 2:15 pm

Poland Spud do this same test with your uC to see how noise immune your micro controller is. Let me know your results.
not sure if you remember but I did abuse it quite a lot here
[youtube]http://www.youtube.com/watch?v=V3Akt3SKhAs[/youtube]

my desktop was like 4 meters away or so and when the ignitor discharged the PC somehow had problems with devices connected to its USB ports (in the background you can hear the sound which is played whenever a new (and unknown device is plugged into the USB port))

Not only that - the uC occasionally freezed - you told me to include a cap in the circuit and after that the circuit was working fine (though the desktop still behaves in the same way ;D)
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Unread postAuthor: dewey-1 » Wed Mar 06, 2013 2:24 pm

I remember that. That is some extreme RF being generated with a HV arc.

If your circuits can survive the "drill test" at 6 inch proximity they will typically survive a normal ambient environment like your home.
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