buying advice shift registers

hi there

I’ll buy some shift registers in the near future and would like to ask which one
I should buy… I’ll certainly go for the 74HC595 but which version. There is one
with DIL-16 and one with SO-16 enclosure. I unfortunatly don’t know what that
means… can anyone help me?

(oh by the way, is it normal that white LEDs are alot more expensive than all
the other colors?)

best
yves

hi there

I’ll buy some shift registers in the near future and would like to ask which one
I should buy… I’ll certainly go for the 74HC595 but which version. There is one
with DIL-16 and one with SO-16 enclosure. I unfortunatly don’t know what that
means… can anyone help me?

You want DIL-16, because the SO-16 are very,very small therefore hard to solder especially if you are a beginner in electronics.

(oh by the way, is it normal that white LEDs are alot more expensive than all
the other colors?)

Yes.

Eberhard

thank you!

To clarify, the DIL package is the style of the ATMEGA chip on your Arduino and the SO package is the style of the USB driver chip.

For your LEDs look at www.ledshoppe.com. They have white LEDs, a package of 100 for $10 including shipping, and if you sign up for the newsletter, they’ll even through in a keychain laser pointer/flashlight.

I’ve bought from them and they seem to have good customer service as well as good products.

thanks for the clarification. yeah, if it’s the same as the usb chip, phew, that’s small.
I’ll go for the other package. and the store looks good, thank you!

ok, and another question… I don’t want to spam the board, so I’ll ask here:
Is there an easy way to calculate the approximate time arduino runs on battery?

I’ll use around 50 leds. I remember there was some kind of a formula. I should
be able to calculate this if I know what kind of battery I’ll use and how much the
LEDs need, right?

sorry for the newb question…

best
yves

ok, and another question… I don’t want to spam the board, so I’ll ask here:
Is there an easy way to calculate the approximate time arduino runs on battery?

I’ll use around 50 leds. I remember there was some kind of a formula. I should
be able to calculate this if I know what kind of battery I’ll use and how much the
LEDs need, right?

It depends on the batteries as well as what’s being powered.

For AA recharable NiMH batteries, you have around 2 amp-hours. An LED takes about 20 mA and the Arduino takes about 20mA. So if you had all 50 LEDs on at once, you’d be using about 1000mAh, and the batteries would last about 2 hours.

thank you! I might have to rethink my concept then. It’s supposed to be some kind
of a wrist watch ;D .

best
yves

thank you! I might have to rethink my concept then. It’s supposed to be some kind
of a wrist watch ;D .

In the pre-LCD days, there were LED wrist watches. The way they solved this is that they were off all the time. There was a button to make the display come on for a few seconds. There were also more advanced versions that had motion switches so you could swing your arm a certain way to get the display to come on.

sounds good, I’ll look into that! :wink:

http://www.dipmicro.com/store/index.php?act=viewCat&catId=28

For cheap items, including Leds and a lot of other cool stuff.
It’s especially good if you live near/in Canada.

I unfortunately live in europe, switzerland. any good advice for that region?

Hi,
if you have problems finding a local shop here are 2 german distributors :

Segor : http://www.segor.de/ Actually the distributor for the Arduino over here, and all sorts of electronic components.

Reichelt : http://www.reichelt.de/ In germany its probably the cheapest online shop for electronic components. (But check with Segor on individual items.)

Eberhard

I live in switzerland, any good advice for that region?

Travel to Zermatt and do the hohbalmen hohenweg :slight_smile:

But for parts, have a look on ebay, particularly if you want to buy in quantity and don’t mind waiting a week or so for items to be shipped from china.

You could also try dealextreme, they have a eclectic range of LEDs, such as:

20 packs of red, green or orange for $2.35 each including shipping
http://www.dealextreme.com/details.dx/sku.11099
http://www.dealextreme.com/details.dx/sku.11100
http://www.dealextreme.com/details.dx/sku.11101

or this 60 lumen! white emitter for $2.75 including shipping.
http://www.dealextreme.com/details.dx/sku.13286

hi

thank you for these suggestions. I have two shops in switzerland but they
are not very cheap and lack certain items.

what kind of resistors do I need? I thought the ones I got with my
arduino kit are coal resistors. but the shop I have here lists them starting
at 1W. But I would need one at around 0.33W.

now they have also metal oxyde resistors, but they seem to be much more
expensive. is that possible, or could it be an errpr in the shop system (they
list the price per 1 resistor, where the coal ones are listed as per 100 items).

for the german speaking readers, this is the shop I’m talkin about, maybe you
can help:

https://www.distrelec.ch:443/ishopWebFront/catalog/node.do/para/language/is/de/and/shop/is/CH/and/id/is/01/and/node/is/acababafac.html

thanks so much for your help!

Metal oxide resistors have better temperature stability and can be more reliable in the long term compared to carbon, but that probably doesn’t matter in your application. I am not sure how much current you want to put through your leds but the .25 watt 5% carbons on that site should be ok for 50ma to 100ma depending on the LED voltage drop

How did you arrive at the .33 watt figure?

I used the following formula to calculate the ohms:

Basically though, if you want 20mA, the resistor should be ([supply voltage] - [led voltage]) / 0.02. Or 50*(supply voltage - led voltage).

So I calculated: 5V - 3.5 (led voltage) / 0.02 = 75 ohms

=> P = V^2/R with this formula I get around 0.33 watts?
Is this not correct?

About the 0.25w items on that site: what I don’t understand is why there are several items available
starting from 1 W upwards. Is not this one the actual resistance value?

best
yves

=> P = V^2/R with this formula I get around 0.33 watts?
Is this not correct?

The power dissipated by the resistor is the voltage drop across the resistor squared divided by the resistance = 1.5^2 / 75 = 0.03 (or you can compute P = IV = 0.02 A * 1.5 V). The rest of the power is dissipated by the LED, mostly in the form of light. This power is computed by P = IV = 0.02 A * 3.5 V = 0.07 W, for a total resistor-LED power dissipation of 0.1 W.

  • Ben

I used the following formula to calculate the ohms:

Basically though, if you want 20mA, the resistor should be ([supply voltage] - [led voltage]) / 0.02. Or 50*(supply voltage - led voltage).

So I calculated: 5V - 3.5 (led voltage) / 0.02 = 75 ohms

=> P = V^2/R with this formula I get around 0.33 watts?
Is this not correct?

The formula is correct. Though, since you know both the voltage and the current through the resistor its easier to use
P=UI=1.5V0,02A=0,03W

But as you can see you got the actual calculation wrong. It’s 0,03W not 0,3W.

About the 0.25w items on that site: what I don’t understand is why there are several items available
starting from 1 W upwards. Is not this one the actual resistance value?

best
yves

Since all the values given in the table are typical resistor values they got an error in their database. The values should read 1Ohm, 27kOhm, 560kOhm etc.

But I’m not sure about the prices, looks like you have to order a minimum of 1000 Resistors per value? (that would almost match the prices in Germany 5? if you order >=1000)

Eberhard

So I calculated: 5V - 3.5 (led voltage) / 0.02 = 75 ohms

I believe the mistake he was making was to use the full 5 V in the power calculation rather than the voltage drop across the resistor. This leads to:

P = V^2 / R = 25 / 75 = 0.3333

  • Ben