Hero999

All that means is that if the capacitor is too small, it won't be large enough to damp the oscillations but if it's a single, large value capacitor it won't be good either. Higher value capacitors tend to have poor high frequency characteristics and become inductive past the resonant frequency, the higher the value, the lower the resonant frequency. Rather than using a single, high value capacitor, it's better to use a large capacitor and lower value capacitor in parallel with one another. The type of capacitor is also important; for example tantalum is better than electrolytic. I'd recommend a 1uF tantalum in parallel with a 100nF and 10nF ceramic capacitor on both the input and output. If you don't have a 1uf tantalum, go with 22uF electrolytic.

Yes, a Schmitt trigger will certainly work. If you use a comparator IC such as the LM311 or LM393 you can fine tune the hysteresis band to get the best results.

You could have answered that yourself if you had bothered to read the first two links I posted previously.

You may get more help if you provided more information, such as what the device actually is? You could put ORing diodes after the regulator and if you're cleaver you can configure it so it only looses a diode drop when running off the battery. Oh and the LM7812 needs between 2V to 3V to regulate properly, 1.2V is much too low.

The value isn't critical. I'd also recommend adding a 100nF ceramic capacitor to the output as it has better high frequency characteristics. The addition of capacitors is known as bypassing or decoupling and it touched on in the LM7805 data sheet. http://www.ti.com/lit/ds/symlink/lm340-n.pdf A more detailed explanation can be found on the LM317 data sheet. http://www.ti.com/lit/ds/symlink/lm117.pdf Here are a couple of links with more information: http://www.ti.com/lit/an/snva020a/snva020a.pdf http://www.ti.com/lit/an/snva558/snva558.pdf

If you expect good marks then you should build it properly. I recommend calling this the first prototype then building it again more neatly. It's not just a fire risk but a shock hazard too. The cables are so poorly soldered a live mains wire could easily break off and touch the case causing it to float at mains potential. Where's the mains earth connection? If you've not got one it's doubly dangerous and if you have then it could easily break off. Both parts of the case should be connected to mains earth/ground with a longer wire than the live and neutral so it's the last to break if the mains cable is pulled out. Where's the mains fuse? Fine, it hopefully won't catch fire if it's working properly but what if there's a short circuit? The wires could heat up, causing smoke and fire. This is much more likely to happen as you've constructed it so poorly. There should be a mains fuse on the primary of the transformer and it's also a good idea to put one on the secondary side too. Then if there's a short circuit it won't catch fire. In this case the fuse should be slow blow and 1.5 times the fully loaded current taken by the transformer.

Why bother making your own power supply if you do it badly? You can probably get a crappy cheap Chinese power supply off ebay for much less than it cost for all of the parts and it'll be much more reliable too. You'll be lucky if it doesn't catch fire or electrocute you.

We can't help you if you don't provide any information.

Assuming Vcc is the same as the voltage powering the MCU, as a general turle of thumb, make the base resistor 10 times the value of the relay's coil resistance.

A safety feature of battery management systems is to refuse to charge the battery again once the voltage has dropped below a certain level. The only way round it is to reset the battery management system.

How much are you willing to pay for someone to design it for you?

Oh so basically you're looking at building a battery powered 5V PSU with USB sockets? If would work of course but why use lithium ion cells? If go for 4 NiMH C sized cells which have a similar energy density but are safer and have the added advantage of being able to be charged by a standard NiMH charger.

It sounds like the secondary voltage on the flyback exceeded its maximum rating causing the insulation to fail, arc over and internally short circuit. The only fix is a new flyback. To prevent this from happening again do the following: add more turns to the primary or reduce the power supply voltage and never operate the flayback open circuit.

What's an LED scanner? Don't you mean a sequencer of chaser? Two CD4017s and some transistors could be used to do this.

What do you mean by a classic motor and why do you want to do this? Stepper motors have poor torque and lower speed compared to DC motors.

What do you mean by this? Please provide more information.

Thanks for posting your circuit. Just a few suggestions: Why use relays? Surely it'd be better to use DPST switches instead. Maybe if it's a large motor relays are the best way to go but in this case it's a small motor so could be switched directly. You could then use normally closed limit switches.

Why no tbuy one if you've got no idea of how to make one? Electrically speaking, this isn't a very complicated project. It's the mechanical part which is probably the hardest.

I suggested using a latching push-button so that wouldn't happen. A non-latching push-button would be no good here because the curtains would draw when it's pressed and open as soon as it's released or vice versa, if it's wired the other way round. No, to do that you need two SPDT push-button switches: one for open and the other for close or you could use a rocker swithc with a spring return to the centre position, like a car's electric window switch.

It sounds pretty straightforward, what part are you having problems with? I would consider replacing the lamps with LEDs because they use less power, can be run off a safe/lower DC voltage, last for longer than incandescent lamps (especially when flashed) and turn on/off instantly. I wouldn't recommend having nasty mains voltage anywhere in your circuit, it's much safer to power the whole thing from a PC or laptop power supply. If you insist on mains, an AC lamp can be controlled with DC power via a TRIAC and an opto-isolator. I'd advise using an opto-coupler with zero crossing as it's easier on the TRIACs and will generate less RF interference. Relays aren't suited to this application because they tend to wear out very quickly when switched at this rate. If you're using mains, there must be at least 7mm of clearance between the AC side and DC control voltage. The sequence can be generated using a ring oscillator, a microcontroller or an oscillator with a CD4017.

On second thoughts this is easy with switch/relay logic. The motor can be reversed by exchanging the positive and negative connections. The simplest way to do this is with a DPDT switch. Normally closed limit switches can be used to disable the forward/reverse direction appropriately, so when the motor reaches the end of its travel it shuts off. The trouble is a latching DPDT push-button switch doesn't seem to be a common part. If you can find one then good but you may have to combine a DPDT relay with a standard SPST latching push-button, although it's not ideal is it does draw a lot of power, even when the motor isn't running so is useless in a battery powered application.

If it's that easy than why haven't you figured it out for yourself yet? I don't know how you can do it because you haven't provided enough information. What kind you motor are you using: DC, AC shaded pole/synchronous? What components do you have at your disposal? This requires a state machine which isn't easy to implement with relay logic but is trivial with logic ICs or a microcontroller.

http://uk.farnell.com/emerson-network-power/da12-050eu-m/psu-plug-top-5v-12w-eu/dp/1886221 http://uk.rs-online.com/web/p/external-power-supplies/7210914/ http://www.e-plenish.com/pgProduct.cfm?Product=10687_156_353263-V930650-SVUSBPOWERUK-StarTech_com_SVUSBPOWERUK_AC_Adapter_5_V_DC_2_A_For_KVM_Switch http://www.maplin.co.uk/ac-dc-fixed-voltage-switched-mode-power-supplies-48484

My advice would be to use six batteries in series and a switch mode buck regulator to reduce the voltage to 5V. If you don't have room for more batteries then use AAA cells instead but bear in mind the capacity will be lower. A SEPIC converter can generate 5V from 4V to 6V but it's a bit harder to make than a buck regulator for which there are many ICs available.

You need a voltage regulator to convert the 4V to 6V from the batteries to a stable 5V supply for the USB devices. I seriously doubt the batteries you've bought are really 3800mAh, they're probably more like 1000mAh.