hackduino help please!

hey guys i’ve really exhausted all my options so i’m reluctantly turning to all of you for some expert advice - following a couple of different instructables i was able to cobble together my own compact hackduino but it’s dead in the water… as you can (hopefully) see from the attached pic it’s powered by no blinking led :frowning: the chip is preloaded and works perfectly in my actual arduino… not sure how well the pics show detail and will be happy to provide more info if you think you can help :slight_smile:

guys, please don’t jump down my throat as i’m really just a beginner (obviously) and and doing my best to stand on my own two feet but i gotta learn to crawl before walking (and running)… thank you all for whatever assistance/guidance/expert advice you can offer!..

  • max

Decoupling capacitors on your Vcc/GND pins? (or the lack of rather?)

Like majenko said, try putting in the 0.1uF decoupling capacitors. Also, make sure the crystal can does not short against the leads of the load capacitors (which should be about 20pF).

Did you verify the supplly voltage?

What is written on your 20pF capacitors?

Take the 328 out of the I.C. socket and plug it straight into the Porto Board (with the power off).

EDIT: Believe it or not I have had LEDs made with the leads reversed, the yellow LED looks OK but try to turn it around to see if you have one of these freaks. Or try it instead of the power LED to see if it is OK. Also try a .1uF capacitor on the i/p of the regulator rather than the one you have.

you guys rock!!! thank you all... not sure which one of those suggestions did the trick but it worked!..

here's a follow up - now i have my servo connected but i'm getting only about 4.6v and need at least 4.8... at least that's what i think the problem is because when i plug in my usb it runs but with 4aa it's dead as a door nail... any suggestions?..

  • max

Power your servo from a separate supply. Connect the grounds of both supplies to each other. Do not connect the positive voltages together. Your servo probably draws too much current.

i'm trying to keep the overall size/weight/number of components to a minimum... i prefer to power the entire thing using 4aa batteries... not sure if i'm missing or not understanding something but my impression was that this was sufficient for this servo (hitec continuous rotation) with a minimum operating voltage 4.8v... but for some reason i'm getting slightly less... anything i can do short of separate power supply?.. thanks again!..

  • max

Is that a LM780x regulator on the breadboard ?

How are you connecting the USB? Bypassing the regulator?

MAS3:
Is that a LM780x regulator on the breadboard ?

Quite probably - that seems to be the default for all Arduino projects. Simple to use, but a bit naff really by today’s standards.

6V into an LM7805 isn’t going to cut it. 6V - 2V (yes, the data sheet specifies a dropout voltage of 2V!!!) is only 4V. So, you want to either increase it to 5 AA batteries, or change to a more modern regulator with a lower ( < 1V ) dropout voltage.

@MAS3 and @majenko - you nailed it... i read a few different instructables and they all use LM7805... what would be a good choice for a "regulator with a lower dropout voltage"?.. and will it be safe for the rest of the circuit components or will i need to somehow reduce voltage to keep stuff from frying?..

Dropping the voltage is the whole point of the regulator. If you had to drop the voltage as well some other way, what would be the point of the regulator? The only times you'd want to drop the voltage outside the regulator would be if you wanted to spread the heat load between multiple regulation stages (24v down to 12v down to 5V for instance) or if your input voltage was above the input voltage of the regulator.

Which one to choose all depends on how much current you think you need.

If your needs are small (a couple of hundred mA) then the MCP1825S-5002E/AB is a good choice - drop-in replacement for the LM7805 and only 210mV dropout voltage. It can only go up to 500mA though, and limited to a 6V maximum input voltage (fine for 4xAA).

For larger current needs, you might look at the LF50ABP from ST. It can provide up to 1A, and can run from up to 16V, but the dropout is slightly higher at 400mV (still well within our parameters). Again, it's a drop-in replacement for the LM7805.

There's many more to choose from, as well. The parametric search facility on your favourite supplier (farnell, RS, digikey. mouser, etc) will help you find a good one.

again, i have to say i'm very impressed with this board!.. thank you all for your input!..

@majenko - my plan is to have an ir receiver and hitec cont. rotation servo that'll run for about 3 seconds every time a button on a remote is pressed... in my humble opinion MCP1825S-5002E/AB should do the trick, right?.. and just to reiterate: higher voltage (ie smaller drop) will NOT have any adverse effect on the chip etc, correct?.. just don't want to jump from a frying pan into a fire :)

The “dropout” voltage is the minimum voltage difference between input and output. You can think of it as the portion of the voltage that the regulator consumes for itself.

Here’s an example.

Scenario 1:

A certain 5V regulator has a dropout voltage of 2V.

You provide 8V as an input voltage.

The regulator consumes 2V internally, leaving 6V.

The regulator regulates that 6V down to 5V by converting (6 - 5) 1V into heat. (Yes, the “consumed” 2V is also converted into heat as the regulator does stuff - this isn’t “real”, just an illustration of what the dropout voltage means, so pedants keep silent.)

Scenario 2:

A certain 5V regulator has a dropout voltage of 2V.

You provide 6V as an input voltage.

The regulator consumes 2V internally, leaving 4V.

The regulator is unable to regulate the voltage to 5V as 4V is below the desired regulated voltage (a linear regulator can only regulate down, not up). Therefore the output voltage is below 5V and unregulated.

So basically the “dropout voltage” is the minimum amount the input has to be above the regulated voltage in order for the regulator to work.

got it!.. @majenko thank you for explaining it...

ok, so i plug in MCP1825S-5002E/AB instead of 7805 and supply approx 6v via 4aa batteries... i will now have sufficient voltage (about 5v) to run my servo... but will this voltage be too high for the rest of the circuit or my 328?.. i assume there's a legitimate reason every one of those instructables refers to 7805... or am i overthinking it?..

  • max

maques_n_la: got it!.. @majenko thank you for explaining it...

ok, so i plug in MCP1825S-5002E/AB instead of 7805 and supply approx 6v via 4aa batteries... i will now have sufficient voltage (about 5v) to run my servo... but will this voltage be too high for the rest of the circuit or my 328?.. i assume there's a legitimate reason every one of those instructables refers to 7805... or am i overthinking it?..

  • max

The 7805 is used because it's "common" and the default option for people who don't know better - a bit like a TIP120 or an LM714.

It gives 5V out, which is being used to power your '328 circuit. The same can be said for the MCP - it gives 5V out, which is being used to power your '328 circuit.

The '328 can run off up to an absolute maximum of 6V, so even without a regulator in there it would still be (just about) fine. 5.5V is the recommended maximum, and of course, 5V is happily below that. (if it weren't then none of the AVR Arduinos would work, as they are all 5V).

@majenko - you rock!.. thanks again for your patience... i realize it's probably pretty frustrating to spoon feed newbies so i appreciate it...

off to radio shack!.. btw, should rs not carry it, what would be the next best thing(s)?..

well, i'm at a loss... while trying to locate a more-appropriate regulator i experimented with more batteries... now i have 12v supply and am getting about 5v going to my hitec servo... but it's still dead!.. if i hook up parallax servo it actually buzzes for a moment as it comes to life but that's about it...

any suggestions?..