I'm will be using a 555 timer and want to hold or lock the signal.

[slim_jim_56]

First ... I am a complete newbie who by accident was able to fix my monitor by finding and replacing a bad (but still looking good) capacitor. So now I'm hooked on electronics and am trying to understand different circuits. So.... I want to energize a coil to counteract a magnetic attraction. I have seven coils and want to be able to control the timer by using a variable resistor. So far so good. I want to power coil 1 until coil 4 is powered. ditto coil 3 until coil 6 is fired. and on around until I get back to coil 1. I want to use the pulse that energizes coil 1 to shut off or unlock the power to coil #4. The coils will fire in the order of 1,3,5,7,2,4 and 6, then start over. The speed of firing will be controlled by the VResistor. Can I use two NAND gates to fire up coil #1 and then have the pulse from the firing up of coil # 5 shut the power down.
I am over my head already but I'm trying to figure out if it can be done.
Thanks
Slim_Jim (And that's not accurate either)

 

[(*steve*)]

Perhaps you could start by telling us what "magnetic attraction" you're trying to counteract, and why it is that you need 7 coils to do that.

As a complete newbie (your term) it is better to tell us what the problem is than to tell us what your solution is. If your solution is wrong, we may lead you to producing something that operates correctly, but fails to work.

 

[slim_jim_56]

Good advice. I am playing with a rotor with 4 permanent magnets mounted to it. I have 7 electric magnets on the stator and I am trying to get the rotor to start and spin by magnet force. The permanent magnet should be attracted to the core of the electro magnet but when it gets to it I want to give the electromagnet enough of a current to break the attraction so that the permanent magnet will swing on by and get attracted to the next core and start pulling toward that. Having 4 magnets on the rotor and 7 electromagnets on the stator, one magnet will be over a core and another magnet will be almost past the core, which will leave two magnets pulling forward toward anther two elctromagnet core. So the electromagnets need to be neutralized while the rotor magnets are directly over them and need to stay powered up until the magnet is far enough past to become attracted to the next electromagnet core.
Because I want to be able to control the speed, the timing will speed up and the amount of time the electromagnet will stay powered will reduce. So I thought that the whole thing could be controlled by powering up one electromagnet and using the same pulse of the 555 to power down a different electromagnet. The pairs will be
1on/4off _3on/6off _ 5/1_ 7/3 _ 2/5 _ 4/7 _ 6/2 _and 1//4 again in repetition.
Coil 1 will remain on until coil 5 is started.
Coil 3 will remain on until coil 7 is started etc.
That's my project. Its all in my head at present but I can't get the picture of what I need to do to get the pulse from the 555 IC so it will make the power come on and stay on and then be shut down. I plan to use a 4022 chip (A divide by eight chip) to isolate the 555 pulse to be used on each of the seven coils.
Jim

 

[(*steve*)]

my advice would be to look at an oscillator (555 is OK, but maybe one made from a schmitt trigger linked to a 4017 with the 8th output connected to reset.

This will turn on the outputs 1 to 7 in sequence and then start again.

I would start by powering the coils one at a time, so you power one, then the next that has the rotor just approaching it, then the next, and so forth.

The outputs of the 4017 would not be able to drive the electromagnets directly, you would need to use a transistor (at a minimum) to switch the load.

 

[slim_jim_56]

Thanks Steve. I am with you so far. How do I use the signal from the 4017 to power one transistor and keep it powered and also shut off another transistor. Is there a way to "lock a transistor in the "on" position until another signal trips it off?
Jim

 

[(*steve*)]

Is there a way to "lock a transistor in the "on" position until another signal trips it off?

Well, anything's possible, but it's probably not what you want.

The easiest way is to connect the outputs of the 4017 to the bases via diodes. That way you can have the transistor turned on when any set of 4017 outputs are on.

For example, you could connect outputs 1, 2, and 3 (via diodes) to one transistor, and 2, 3, and 4 to another transistor, and so on. That would keep a series of three transistors turned on as the counter moves from 1 to 7.

The more transistors you want to turn on at once, the lower current you can apply to each, so you'll need either high gain transistors or darlingtons (also the base resistor becomes more important to ensure that all transistors get turned on evenly).

Honestly, I'd start with 1 turned on at a time to make sure it works, then add additional complications later. It may be easier to start with LEDs rather than the coils (and a low frequency oscillator) so you can visually see what is happening.

remember when you get the transistor to drive the coils that you need a diode in parallel with the coil to prevent large voltage spikes from damaging your transistors.

 

[slim_jim_56]

Steve, thank you for your insight. I have only been "into" electronics for about two weeks so I need to digest and research what you are sharing with me so that I can understand what you have shared. Please look for my ?s in the future.
not so 'slim_jim'

 

[(*steve*)]

Here's a few things to look at.

this http://www.kpsec.freeuk.com/components/ic.htm has some background material. You should try to become somewhat familiar with it as the 4017 I have suggested is a CMOS IC and this page has some warnings about them (they're static sensitive). Ignore the stuff about 74HCT and 74LS if you want to as it's not particularly relevant.

Also check out the datasheet for the 4017. The manufacturer includes lots of information and often suggested uses. Some of the stuff will be way over your head, but check out how it's used (bugger -- they don't include application notes). Also note that power supply connections are rarely shown in their circuits but are vitally important! Ensure you know what voltage the device requires. http://www.datasheetcatalog.com/datasheets_pdf/4/0/1/7/4017.shtml

Check out the "Nite-rider" LED display here http://www.qrp.pops.net/LEDs.asp -- it uses a technique that I suggested, although in a simpler way. Perhaps you can build one of these on a breadboard to experiment. Note that this circuit has no resistors to limit the LED current. It relies on the fact that CMOS can only supply a limited current. It's a bad idea for a number of reasons. Put a 560 ohm resistor in series with the LED and it will be safe(er) from accidental damage.

Get a breadboard if you don't already have one.

Learn how to use a 555 as an oscillator or use some CMOS schmitt triggers (my favourite)

Remember that unused inputs on CMOS devices must NOT be left disconnected. It is easiest to connect them to ground, but for some devices (say the 4017) you will have to check the correct place to tie the unused reset pin.

Look at this http://www.fairchildsemi.com/an/AN/AN-140.pdf especially figure 8 -- the simplest oscillator you will ever find. As long as the resistor is more than about 10k the output is perfectly acceptable to drive the 4017.

For an oscillator that runs slowly enough to watch the output, you want 0.5 to 2 Hz. The calculation they give you here is far too complex, an approximate equation is 1.2/(R*C) see http://talkingelectronics.com/pay/BEC-2/Page49.html for more info).

if you use a 100K resistor and a 10 uF capacitor you'll get close to 1Hz If you make that resistor a 10K resistor in series with a 100K pot, you'll be able to vary the frequency from about 1Hz to 10 Hz. Use smaller capacitors for higher frequencies.

That should give you plenty of basics to carry on with.

Buy a couple of 40106 and 4017 chips if you have to get them by mail order or take a long trip as you may damage them, and they're pretty cheap. I recommend the 40106 because its power supply requirements match the 4017. Other equivalents like the 74HC14 or 74C14 require exactly 5V and other families (74LS, 74ALS, etc.) have very different characteristics that may make your task less predictable.

 

[slim_jim_56]

Here's a few things to look at.

Thank you Steve. I will look up that info. This is very nice of you to take the time to give me your insight. I really am impressed with all of this. Why didn't I see this in my younger years. Oh well, its a new and exciting hobby.
Jim

 

[slim_jim_56]

Steve, I bought a "Solderless Breadboard & Op Amp ICs Kit #1 (#1230)" online for about $17.00 . Its a Nightfire Electronics kit. So I hope its a good starter kit. If you have any recommendations a long these line I would appreciate it.
Jim

 

[(*steve*)]

Sounds like an excellent start.

With these breadboards you often need to link things together with wire (say to jumper pins together, or connect power to something).

My advice would be to go out and get one metre of cat 5 cable (network cable with solid core wire, not the "flexible" stuff) That will have 8 wires in it. Cut them as you need them into short lengths (could be a couple of cm). That wire is well suited to these breadboards, and ample for the very small currents you're likely to be using.

I would advise that you get a battery holder that holds either 4 or 6 AA cells as these will be cheaper in the long run, and supply more current than a 9V battery.

If you get hold of some CMOS chips, or MOSFETs, remember that they are static sensitive and should be stored and handled appropriately. Generally they will be transported in some suitable packaging, so keep the bag or tube to store them in after use. A suitable alternative is to cover wrap some expanded polystyrene in a couple of layers of aluminium foil and stick the components into this.

When you handle static sensitive stuff, try not to touch the metal pins and work on a surface that doesn't hold a charge (i.e. plastic is bad, paper is OK, special conductive mats are best, but probably not worth the expense at this stage). If you take basic precautions you'll be pretty safe.

If I were you, I'd grab one or two LM555's and a couple of 4017's and maybe a couple more LEDs -- it will probably set you back a couple of dollars. You have 9 LEDs in that kit, but you may want to monitor a few more places. Oh, I'd get a few more diodes (1N4148) and general purpose NPN transistors (2N3904, 2N2222, BC548, etc) -- you're likely to use them for the circuit you want to make. Oh, and you're driving an inductive load, so grab 10 1N4001 diodes.

You can get much of that from Nightfire too. Just make sure that you don't order SMT parts (for ICs they should be DIP-xx, not SOIC-xx)

(I promise I can't think of anything else). None of those components are critical, so if your supplier doesn't have exactly that component, then something similar is just as good.

In most cases you can "cheat" and run LEDs directly from the outputs of CMOS. In other cases where you need resistors, things are often not really critical, so if you run out of one value, use the closest one you have.

If you have any questions feel free to ask.

 

[slim_jim_56]

Many thanks again, I was wondering which type of wire to use for the jumpers. I am awaiting my kit with anticipation. I was planning on using one of my many "plug in" devices that I have around that used to be used to power up disc players and walkmans etc. They have a range of voltages and amperes. Is there any reason that I should not use them for power? Or should I stick with the batteries?
And thanks for the shopping list. I'll pick some up. There is a Radio Shack in town but I have the impression that their components are on the poor side as to quality. Is that a common opinion?
Jim

 

[(*steve*)]

Well, we don't have Radio Shack in Australia, I do have memories of Tandy some years ago. My impression is that their product was 90% packaging.

I'm not sure that quality is the major issue, since their components are as likely as anyone else's to be up to spec. If the cost of buying from them beats the cost of purchasing elsewhere plus freight, then it's a good deal.

Depending on how long you're prepared to wait, there are often sellers of components on eBay that sell moderate quantities of parts at very reasonable per unit prices. (Beware, there are others that are very expensive).

here's some that I came across LEDs, Transistors, 1N4148 Diodes, 1N4001 Diodes, 555, 4017

Depending on your other options, it may be cheaper to get some from eBay if your local options are limited. Digikey is also probably an option to look at. However 1N4001 diodes will cost you around 17c each (in quantities of 10) plus freight.

The quantities when buying from eBay are larger than you're likely to need, and the shipping times may be long (several weeks), so you should only consider them if your local option is MUCH more expensive or if you *really* think you'll use them all eventually.

There is a risk when buying from China (or even from the US!) that you'll get counterfeit components, but for the use you'll be putting them to it's unlikely that you'd even notice.

The main issue is that you are able to read the spec sheets sufficiently well to determine which leads are which so you don't put components in a circuit the wrong way around.

If you purchase some kit of components (as you already have) you will soon be asking yourself some quite sophisticated questions -- "Can I substitute the specified component X for the component Y that I already have". It is a bit akin to choosing bolts -- in some cases it doesn't matter what their tensile strength is, what corrosion resistance they have, or what metal they're made of, or how long they are; however in other cases a very specific bolt is required. Fortunately, for many simple circuits you can replace almost any small signal NPN transistor with almost any other small signal NPN transistor.

 

[slim_jim_56]

Again, many thanks. I'm looking forward to this learning process.
Jim