***Official Electronics Thread of Officialness (it starts off with lots of Nixie Tube Clock goodness

[lord filbuster]

A questions for you guru's!

1) I want to run this electromagnet (http://www.electriclock.net/acatalog/info_ELS_10003_R.html), am I right in thinking a constant 0.5A from a standard 9v battery would keep the magnet "on"?

2) How do I work out how long a battery will last?

3) What would be the easiest/cheapest way to have a button, which when pressed would trigger a random time period (between 1 and 4 seconds) to wait before dropping the current and thus turning the magnet "off"?

Many thanks in advance for any help

That magnet is rated for 0.5A at 12v or 0.35A at 24v. It may still work at 9v, but i doubt you would even get 10 minutes out of an alkaline or ni-mh 9v battery. You might get more out of a lithium 9v, but even then you wouldn't get very long. A regulated 0.75 to 1A 12v power supply is what you want.

Batteries have a rated capacity given in amp hours, so you simply divide the capacity by the current in the circuit. Alkaline 9v batteries are about 0.5Ah, so in theory, it could supply 0.5A for one hour. The only problem is that alkaline will only really give you the full capacity if they are put under light load, say 0.05A for 10 hours.

As for the circuit, a 555 timer and a 4017 counter set up in the right way could do what you are asking for.

 

[Dr.EM]

A 9V PP3 won't supply 0.5A in the first place. You'd be better using a set of 8 AA or ideally C cells in series to provide the 12V supply, or alternatively a small Lead Acid rechargeable.

If it were a lead-acid type, it'll be sold with an Amp-Hour (AH) rating. If it were rated for 4AH, then with your draw of 0.5A you should expect 8 hours operation. The ratings for various alkaline or rechargeable cells should be available in their datasheets though it's not always so clear. Also note that 8 rechargeable cells (Ni-MH chemistry) produce 9.6V, not 12V, but this may be sufficient.

You could use a 555 monostable circuit to produce a time period to hold the magnet in for, using a relay or MOSFET on the output pin to switch power to the magnet. Do you want the time period to actually be different each time though? If so, a PIC or other microcontroller suitably coded may be the simplest option.

 

[Appelhanns]

Apologies guys, don't know why I read it as 9v :S

So a bike battery like this...

http://www.mdsbattery.co.uk/shop/pr...ogle&utm_medium=base&utm_campaign=google-base

...would work ok, and could provide 6 hours of "on" time (3aH)?

You could use a 555 monostable circuit to produce a time period to hold the magnet in for, using a relay or MOSFET on the output pin to switch power to the magnet. Do you want the time period to actually be different each time though? If so, a PIC or other microcontroller suitably coded may be the simplest option.

Ideally yes I would like to have a different time period each time, so from your suggestion, would a freeduino (http://www.nuelectronics.com/estore/index.php?main_page=product_info&products_id=1)

be suitable?

Thanks again

 

[RomanNose]

Arduino nano v3, just arrived. Now I understand why it's called nano. It's flipping tiny!

 

[Appelhanns]

Arduino nano v3, just arrived. Now I understand why it's called nano. It's flipping tiny!

You're not wrong, if anybody could confirm that an Arduino Uno R3 would work fine for what I want, I will buy it now......(and then pester with many more questions once it arrives!).

Anybody recommend a good forum/site for Arduino absolute beginners?

 

[Dr.EM]

I'm sure that Arduino would be more than capable of providing a varying delay on one of its outputs, but I won't be able to help with the code, that's not my strong area. Plenty of people on this computer forum probably can though! You'll also need an external MOSFET or relay switching for the magnet though as the magnet needs 12V 500mA and the arduino will only do 5V at around 25mA.

That motorcycle battery should be fine and provide around 6 hours operation yeah.



I ordered some 7-segs to play around with multiplexing on a PIC. In short, DAMN YOU COMMON ANODE! I was reading this:

http://melabs.com/resources/articles/ledart.htm

Which uses common anode, though I don't think it stricly has to do so, but I ordered them based on that. However, I saw in my PIC book that driving them with a 4511 Binary to 7-seg driver IC frees up enough PIC outputs that I wouldn't need to span more than 1 port, making coding much simpler. What I forgot to do was change my order and now I have common anode which the 4511 can't drive

 

[RomanNose]

Can you just solder onto the legs of the arduino nano? I am connecting sensor and motor wires and I want them to be secure. Someone mentioned using a breadboard, how would that work? Surely the thickness of the wires would have to be exact and I really don't want it to be insecure.

 

[Dr.EM]

The typical use for the Nano does seem to be to push it into a breadboard like a big DIP chip. It'll fit in fine, but for more permanent applications, hmm. I'd have thought that Arduino was never meant as a permanant install and for this you'd be better off with the standalone Atmel or a PIC chip and a programmer. I guess otherwise your best bet is to solder the Nano onto a stripboard.

 

[RomanNose]

The typical use for the Nano does seem to be to push it into a breadboard like a big DIP chip. It'll fit in fine, but for more permanent applications, hmm. I'd have thought that Arduino was never meant as a permanant install and for this you'd be better off with the standalone Atmel or a PIC chip and a programmer. I guess otherwise your best bet is to solder the Nano onto a stripboard.

Is it possible to solder wires onto the legs? The alternative was a pro mini with ftdi to usb, but I cba with mucking around with getting both pieces from Hong kong. I think it came without the legs soldered on so it was probably more suited than the nano. I was thinking of another way though, can you get connectors that will fit onto the legs? I notice some people have done that and you just slot them on the legs. If you can, do you know what they are called?

 

[PermaBanned]

The typical use for the Nano does seem to be to push it into a breadboard like a big DIP chip. It'll fit in fine, but for more permanent applications, hmm. I'd have thought that Arduino was never meant as a permanant install and for this you'd be better off with the standalone Atmel or a PIC chip and a programmer. I guess otherwise your best bet is to solder the Nano onto a stripboard.

I've seen quite a few minimal designs for 'permanent' arduino circuits. As long as you have the full board to program the chips it seems you can make one for less than a tenner.

 

[Tefal]

Is it possible to solder wires onto the legs? The alternative was a pro mini with ftdi to usb, but I cba with mucking around with getting both pieces from Hong kong. I think it came without the legs soldered on so it was probably more suited than the nano. I was thinking of another way though, can you get connectors that will fit onto the legs? I notice some people have done that and you just slot them on the legs. If you can, do you know what they are called?

strip of female pin headers cut up and soldered to wire?

otherwise wrap wire 270 degrees around each leg (tin the wire first if multi strand) then solder onto the leg. will provide a good secure joint and the 270 wrap makes it much easier to take off should you need too.

 

[Dr.EM]

I'm sure it'd be possible to solder onto the legs, but mechanically it's more stable if you solder the Nano onto a small piece of stripboard then solder the wires onto that, naturally cutting the stripboard tracks running underneath the Nano module.

You could use an Arduino in a permanent install, and if you were only doing 1 project I guess it'd make sense as it may be cheaper than buying a programmer. Most of the bigger boards have excessive peripheral components and connectors for this use though, I guess the Nano is actually one that doesn't.

 

[RomanNose]

strip of female pin headers cut up and soldered to wire?

otherwise wrap wire 270 degrees around each leg (tin the wire first if multi strand) then solder onto the leg. will provide a good secure joint and the 270 wrap makes it much easier to take off should you need too.

Will try both of them, I have now realised that I have a blackbox lying around that is quite strong with a few holes in for wires. Perfect for what I am doing.

 

[Tefal]

Will try both of them, I have now realised that I have a blackbox lying around that is quite strong with a few holes in for wires. Perfect for what I am doing.

mounting it ons trip board might be best though, saves having it flapping around on wires as you could screw the board down.

 

[Dr.EM]

Looks like I need a HEF4543B chip instead of my 4511 chip to drive common anode displays. Actually, it looks like rather a nice chip, it can do both CC and CA LED as well as LCD and VF displays, is latchable and can blank the display (also creates potential for brightness control via PWM).

Looks like I can get one from the famous highstreet retailer, though of course it'll be order-in only

 

[PhillyDee]

Looks like I need a HEF4543B chip instead of my 4511 chip to drive common anode displays. Actually, it looks like rather a nice chip, it can do both CC and CA LED as well as LCD and VF displays, is latchable and can blank the display (also creates potential for brightness control via PWM).

Looks like I can get one from the famous highstreet retailer, though of course it'll be order-in only

Farnell do one, Order Code: 386390. The P part at the end is just the package type. P is Plastic.

 

[Dr.EM]

Yeah, Farnell are good but I think only take orders over £20 value, or if not, charge heavily for postage as Rapid do. Otherwise I'd have just ordered some CC 7-segs from Rapid, but don't want to pay another £5 delivery!

 

[PhillyDee]

In that case, tell me which ones you want, Ill order a load in and send you one at cost price + 1st class post. I order from there weekly usually! Email is in trust, not the hotmail one though!

 

[Dr.EM]

That's a good offer actually, probably faster than the highstreet place ordering in. I'll email you later!

 

[Dr.EM]

Hmm, I'm looking on Farnell and the part surprisingly costs about the same as the highstreet store, and will certainly be more with postage on top, unless I went for 5 or more. More surprising is the limited selection of 7-seg displays, I can only find one 3-digit red CC type on there and it's quite dear too! I suppose I'll order it into the highstreet store anyhow, but thanks for the offer, I may contact you in future!