Power a test TTL circuit from USB?

Having not touched any of this kind of stuff for years I'm looking to power a small TTL test circuit which I intend to built on a breadboard. I wondered if I could run it off USB power. In other words, is it feasible to power a TTL cct via a USB lead and USB socket?

I found a "USB Mini B Breakout Board"

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but I'm not sure that the PCB bit of it is necessary and, besides, it's only rated for 100mA (which may be enough but I can't be sure at this stage). If not USB, I guess I should go for a wall wart and a 7805.

So the question is whether there's a good way to power a circuit via USB, or whether you think I should go down the wall-wart or some other route.

Any suggestions?

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James Harris
Reply to
James Harris
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Sure, that'll work. But why on earth use TTL in 2018?

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

They can only claim 100mA as that's all that USB guarantees without some sort of complicated negotiation. in actual use It can probably do

500mA or more (not that soldeless breadboard is suited to currents above about 200mA)

USB-shaped "phone chargers" that produce 5V at 500mA or more are easily had.

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Reply to
Jasen Betts

TTL, 0.1" through-mounts, and and bipolar transistors are all I know. I told you I hadn't done this for years! What would you recommend 'these days'?

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James Harris
Reply to
James Harris

I've been trying to work out USB power negotiation without much success. I recognise that an un-negotiated port can draw 100mA and I know that a device can negotiate for more. I am not clear, though, on whether there's a cable or a particular outlet which will allow higher current to an endpoint which doesn't do negotiation.

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James Harris
Reply to
James Harris

It all depends on what you are trying to do.

Check ou the Arduino. They are very small microprocessors so to speak. You can get them from China off ebay for $ 2 or $ 3 each. Very simple and easy to program from a computer. You can get a small PC board with one on it and about 20 pin outs. Some can be used for analog input and some for 0 or 5 volt output.

To program them you just plug in a cable from a computer USB port to the port on the Arduino board. It will often power up the circuit too.

Check out Youtube for many things that can be done with them and a few external components. Many programs are already out for them to do many things.

Reply to
Ralph Mowery

HC for slowish stuff. TTL is vaguely similar but sucks power.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

It seems to me that hardly matters unless you plan to run the final device off battery power, or put one in every home. Admittedly the

100mA USB limit may be a factor if there are a decent number of chips involved, but that's just one option for power.
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Reply to
Computer Nerd Kev

100mA (or 150mA for USB 3) is the default limit that USB is _supposed_ to restrict devices to before they request more power. In practice this is often omitted from computer motherboard designs to save cost, but obviously they don't advertise this.

Many USB charger plug-packs don't restrict current, so they might be easier as all you have to do is look at the current rating on the sticker (sometimes this is only enough for the device it was originally intended to be used with, rather than to conform to any particular USB current limit).

Looking more boardly, there are lots of switch mode plug packs without USB connectors, but which provide regulated 5V up to a specified current, so they are an option too. Make sure they're switch-mode, not transformer types (which I think you're already aware of).

See "Low-power and high-power devices" here:

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Reply to
Computer Nerd Kev

Depends on how complicated the circuit is. BITD I used to do boards full of the stuff, and the power consumption was a serious issue. I was doing frequency synthesis for early civilian direct-broadcast satcom, so it had a bunch of 74S and early 74F parts. They sucked, but nobody but the military could afford all-ECL systems.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

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