I was thinking what's the cheapest/easiest way to take a voltage and step it down... eg 5v to 3v
a 4050 should do it, but they're a bit pricey! off of ebay? scam? I think I could just stick to using individual NPN's with a Zener diode. I could hand solder an array of transistors onto a board and sell them cheaper than a few 4050s from ebay lol
ah, I found the chinese! - much better pricing, but even so.... for curiosity sakes.
its debatable if its cheaper/easier, but I use potential dividers instead. Mainly because I've got piles of resistors scattered around.
cjdelphi:
I was thinking what's the cheapest/easiest way to take a voltage and step it down... eg 5v to 3v
5v to 3V -- optocouplers can do it
Bidirectional?
See page 44 of the following
http://i2c2p.twibright.com/spec/i2c.pdf
What's the context?
Speed? Current? Other considerations?
Just like anything else it comes down to context, context, context...
I use these to step five pins down from Arduino 5V to the 3V needed to run those Nokia 5110 LCDs. They work great for that.
19 ways to levelshifting
@1ChicagoDave: What's 'these' for you ?
For the 4 Nokia5110 Signals I use 3 * resistor voltage dividers and 1 * led eating 2V, signaling data transfer for debugging reasons.
work great for that
CD4050 at Tayda $0.24, not to bad a price.
michael_x:
@1ChicagoDave: What's 'these' for you ?For the 4 Nokia5110 Signals I use 3 * resistor voltage dividers and 1 * led eating 2V, signaling data transfer for debugging reasons.
work great for that
That sounds like a pain.... :~
I meant the 4050 Hex Buffers the original post mentioned & linked to.
More specifically —
http://www.nxp.com/documents/data_sheet/HEF4050B.pdf
This has worked for me:
4050 is 52 cents on digikey
A led and a resistor are 2ct each => 20ct for 5 signals, so rather comparable.
Thanks for clarifying, 1ChicagoDave.
Additionally:
Well, all datasheets always say
input voltage ?min -0.5?max Vcc + 0.5 V
Even the nxp sheet you linked, although mentioning at Features "Accepts input voltages in excess of the supply voltage"
We do not need 15V, so any 4050 e.g. 74HC4050 with Vcc 2 .. 6 V should do as well, running it at Vcc = 3V with Vi signals in 0..5V ?
I'm not too familiar with electronics, but I can calculate resistor voltage dividers and leds, and I have a big bag of those 
michael_x:
A led and a resistor are 2ct each => 20ct for 5 signals, so rather comparable.An LED and a resistor use about 20mA each => 100mA for five signals.
4050 uses about 4 microAmps supply current.
That's a ratio of 25000:1 in power cost. $)
(I'm sure there are other losses involved, too. But still substantial difference.)
Again....context—
If just prototyping/testing something or making a single device for yourself that will be plugged into an outlet forever.....use either way. I wouldn't (likely) buy a special chip just for that either.
If designing something which needs to run off a battery, or shouldn't be constantly glowing with the light of five LEDs, or needs to be as small as possible for any number of reasons....maybe go with IC.I'm not too familiar with electronics, but I can calculate resistor voltage dividers and leds, and I have a big bag of those
Yep. Use what you have, what fits the application, and what works best for you (.....or the person using the device).
Thanks, 1Chicagodave.
I don't run 5 leds, but one ( to test indicate data transfer to the 5110 ), and with a 1k resistor it's rather 3 mA than 20 mA ,
but you are right that there's a difference between a test / prototype and a battery driven device used by other people.
I wonder about that usual datasheet line
input voltage ... max Vcc + 0.5 V
which prohibits 5V signals to a 74HC4050 running at Vcc = 3V. (?)
But as this line is also found in your nxp HEF4050B datasheet where there's explicitly the sentence about
Accepts input voltages in excess of the supply voltage
I'm a bit confused.
I think the limit comes from something like this
Vcc ---o--+----
_
^
|
Vi ---o--+----
|
_
^
|
Vss ---o--+----
inside the IC, which would short Vi to GND or Vcc if outside the allowed limit.
???
Thanks for more info on this issue.