Anyone got some 74HC08's lying around?

[admin]

DIPs only please!

Also looking for regs, 78L05 and 78L33.

[JimmyM]

AND gates yeah? 5v?
prety sure i do - ill check me box when i get home - gimme a text this evening to remind me.

dont think ive any regs though.

[JD]

Haven't even seen a 74 series device in a decade. They were my bread and butter back in the day. Out of interest, why the HC variant? You running something of battery?

[Damien M]

What kinda yeast is 74HC08? 
What its attenuation? Group Buy anyone!  :
Chips!! should this not be in the Food Board

[Damien M]

He He! I normally go the the Quadanchip Meself!!

[JD]

HC = faster and lower power. LS used be the default choice, now it's HC.

I want to use it to step up a 3.3v chip output to a 5v chip input, as one chip is 3.3v and the other is TTL.

TTL input voltages require an input to be over 2V to be considered a HI and under 0.8V to be considered a LO. Your 3.3V circuit will typically be CMOS so I'd be surprised if it cannot drive TTL directly.

The problem area interconnecting 3.3V and 5V is when a 5V signal is used as input to a 3.3V device.

[Will_D]

I have two:  74LS08 in DIP package - any good?

LS = Lower Power Schottky iirc

you can surely still buy the regs in Maplins?

[Damien M]

Cheers Will and Jimmy.

Anyone have any of these lying around at work? Don't like to be raiding people's personal stashes.

Eh! This is normally you, bu!!! And just to toe the Clup line "The NHC does not Condone or support any missappropriation of materials for the personal use of its members" 

[JD]

If I connect the 3.3v output to the 5v input it works, but not 100% reliably as it's sharing the bus with other SPI devices. Using an AND gate is the recommended solution.

The 3.3V CMOS output will easily and reliably drive a TTL input under normal circumstances. Since you have a reliability issues, this points to a problem not with the voltage levels, but with the current capacity of the 3.3V output pin. The 3.3V pin hasn't the ability to source or sink enough current when all the extra devices are loading the line. Your suggestion of using the AND gate is to be a buffer that can provide more juice. How successful that can be is down to what you've got driving the SPI bus at the moment.

If you're driving the SPI bus using Arduino outputs, the 74HC08 device might not fix your problem. The Arduino pin can source and sink 40mA. The '08 can only manage 25mA. You might need to use transistors or FETs or look to the devices on your bus to see if they're adversing affecting the current needed to drive the bus. For example, are there too many pull-up resisters in use or are they of too low a value. 

[Will_D]

They are 25p here;
http://www.amazon.co.uk/Spiratronics-74HC08-Quad-INPUT-Logic/dp/B0093Z0WII

[Damo]

Ah...

It's a replicator

Thanks will 

Tube be careful with those, they'll take over

Ps. If carter shows up give me a shout