Messing resistor value of a paper clip

Hi everyone!

I need an 0,3 Ohm resistor for a project for the uni. I have thought to use an paper-clip.

Do you know maybe what a value does it have?

Which is the best way to mess the value? indirect o direct?

Thanks in advance. :)

Maybe: Put three 1 ohm resitors in parallel will give you .33 ohms.

Can order one from digikey. What power rating do you need? http://www.digikey.com/product-search/en?pv1=1343&FV=fff40001%2Cfff80482&k=resistor&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

How much power do you need the 0.3 ohm resistor to dissipate?

As for using "improvised" resistors - ask your instructor's advice on how to measure such a low resistance accurately using the tools available at the university. It is likely that they have something accurate enough to just measure that straight up (even a good DMM can measure that, but you need to be really careful about resistance in the leads, etc). It depends somewhat on how accurate you need the 0.3 ohms to be - and also how much temperature variation it's expected to be exposed to, because that can change resistance (this is spec'ed if you buy resistors - but the resistance variation over temperature is - shockingly - not included in the specs for paperclips)

You do know that resistors are cheap and readily available, right? If you're in the US, get parts from digikey; they have everything and then some, ship lightning fast via USPS first class - $2 shipping that arrives in 2-3 days is normal. To deal with overwhelming number of choices, my MO for buying is filter until only things that meet my needs are in the list (filters should also exclude digireel, tape and reel, and tray from packaging) and then sort by price, ascending.

0.3 ohms is much less common than 0.33.

If you insist on making your own resistors... http://www.troelsgravesen.dk/graphite.htm

A paper clip is not much different from a short piece of copper wire. The paper clip will have less than 0.3 Ohms, but I don't know what the resistance will be.

You'll probably get more resistance at the connections to the paper clip than from the paper clip itself.

A couple of inches of 24AWG NiChrome wire would do it. (Check the Ohms-per-foot specs on your NiChrome wire before trying it.)

The resistance of a normal-size paper clip is roughly 0.3mΩ.

I need the resistor fow this Step-down switch (MC34063).

The resistor is the RSC at the image.

Do you know how can I simulate this? Im trying with PSpice (Orcad) but i dont know how to put a voltage source for Vin with ONLY ONE pin.

but i dont know how to put a voltage source for Vin with ONLY ONE pin.

You can't, a voltage source with only one pin is meaningless. A voltage is the measure of potential difference, with only one pin there is noting to be used as a reference to create a difference.

I know Mike :grin:

I mean how can i put a voltage on the Vin Pin at the Image.??

Pin 4 (Ground) of the MC34063 doesnt appear in PSpice.