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Burngate
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Re: Gertboard Assembly Thread

Mon Sep 24, 2012 5:32 pm

mister_wavey wrote:well, how weird. If I give the motor spindle a helping hand at the start, the gertboard keeps it spinning fine. If I don't give it a help at the start, it just sits there. Rubbish motor?
Friction? Or actually stiction!

That's why it's called a 12v motor, rather than a 9v one ;)

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Re: Gertboard Assembly Thread

Mon Sep 24, 2012 5:37 pm

Sure, but the 9v battery will run it fine standalone...

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Burngate
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Re: Gertboard Assembly Thread

Mon Sep 24, 2012 5:45 pm

mister_wavey wrote:Sure, but the 9v battery will run it fine standalone...
Okay, then it's not an 8v motor!

you had 8v able to keep it running, but not start it, while 9v will start it as well.
Stiction is higher than friction, often by quite a lot.

Generally with something like a motor, torque is related to current, while rpm is related to volts. But when it's not running, the current is limited by the resistance of the winding, so at 8v there seems to be not enough torque to start it.

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Re: Gertboard Assembly Thread

Mon Sep 24, 2012 7:16 pm

carlvk wrote:Today's goal run a servo from the ATmega
Just managed that. :D Today I had a reread of the bits of the manual I glossed over and some measure of understanding is beginning to dawn. :)

This and the table on page 31 helped too :lol:
http://arduino.cc/en/Tutorial/Sweep

By the way, the small servo I used works on 3v3. I thought it might, although it's probably not strong enough for real world apps. :D

Anyone know how to safely rig up a 5V supply to power servo(s)? Do you just give +5V battery to the +ve servo lead and ground the battery -ve to the Gertboard? I imagine that's how to do it, but I'm not going to try that unless someone says it's safe.
Last edited by alexeames on Mon Sep 24, 2012 7:31 pm, edited 2 times in total.
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Re: Gertboard Assembly Thread

Mon Sep 24, 2012 7:19 pm

Burngate wrote: you had 8v able to keep it running, but not start it, while 9v will start it as well.
Stiction is higher than friction, often by quite a lot.
aha - thanks for the explanation - makes so much sense, not sure why I didn't see that for myself...

thx again!

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Re: Gertboard Assembly Thread

Mon Sep 24, 2012 11:04 pm

Hi - new query:

I widened the blink arduino sketch to include the first 4 LEDs, driven from PB5-PB2 and noticed that LED3 from PB3 wasn't lighting (actually it was just barely flickering). I checked the connections and all looked OK. Swapping cables to instead use PB5 to drive LED3 made it light up just fine. I measured 3.33V on PB5 but only 1.2V on PB3.

Using just PB3 alone to light an LED works, as does using it in conjunction with up to 2 other PBx outputs. But when I have 4 or more outputs, if PB3 is included, the LED attached to PB3 doesn't light. However, I *can* light 4 LEDs using any PBx outputs *other* than PB3.

Is this something weird in the chip?

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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 6:45 am

mister_wavey wrote:Hi - new query:

I widened the blink arduino sketch to include the first 4 LEDs, driven from PB5-PB2 and noticed that LED3 from PB3 wasn't lighting (actually it was just barely flickering). I checked the connections and all looked OK. Swapping cables to instead use PB5 to drive LED3 made it light up just fine. I measured 3.33V on PB5 but only 1.2V on PB3.

Using just PB3 alone to light an LED works, as does using it in conjunction with up to 2 other PBx outputs. But when I have 4 or more outputs, if PB3 is included, the LED attached to PB3 doesn't light. However, I *can* light 4 LEDs using any PBx outputs *other* than PB3.

Is this something weird in the chip?
Are you using the LEDs on the Gertboard by wiring into the buffers?

If-so, have you checked them from the Pi?

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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 11:53 am

Not entirely sure what you mean. Using wiringPi's gpio program, I can simultaneously light LEDs 1-4 by connecting GP25-22 to B1-4 and jumpering U3-out-B1 to B4 (i.e. as documented in the manual.)

But when using the ATmega approach, I *can* light any LED using PB3 alone, but I *can't* light any LED from PB3 when 3 other PBx are in use. This is only a problem for PB3; combinations of other PBx pins can light 4 LEDs.

I just wonder what the cause is likely to be. I'd normally assume a bad connection, but the actual chip pin (17, I think, in the ATmega chip schematic on page A-6) registers only 1.2V compared to the other PBx pins registering 3.3V when active.

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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 12:03 pm

mister_wavey wrote:Not entirely sure what you mean. Using wiringPi's gpio program, I can simultaneously light LEDs 1-4 by connecting GP25-22 to B1-4 and jumpering U3-out-B1 to B4 (i.e. as documented in the manual.)

But when using the ATmega approach, I *can* light any LED using PB3 alone, but I *can't* light any LED from PB3 when 3 other PBx are in use. This is only a problem for PB3; combinations of other PBx pins can light 4 LEDs.

I just wonder what the cause is likely to be. I'd normally assume a bad connection, but the actual chip pin (17, I think, in the ATmega chip schematic on page A-6) registers only 1.2V compared to the other PBx pins registering 3.3V when active.
If you've not done so, remove the programming cables from the Pi to the ATmega.

This may be an issue which I'm going to address shortly, however an interim solution is to run

Code: Select all

  gpio unexportall
  for i in 7 8 9 10 11; do gpio -g mode $i in; done
What's happening is that (I think) the avrdude is leaving some of the Pi's GPIO pins as outputs which may be conflicting with the ATmegas...

-Gordon
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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 12:21 pm

ah! nice. thx G.

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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 12:23 pm

mister_wavey wrote:ah! nice. thx G.
I'm assuming that fixed it? If so, let me know and I'll write that into avrdude.

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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 12:26 pm

pulling the wires fixed it. Just putting them back to check the commandline version works too.

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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 12:30 pm

yep, gpio unexportall also worked (naturally). thx again.

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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 12:33 pm

mister_wavey wrote:pulling the wires fixed it. Just putting them back to check the commandline version works too.
OK. Thanks for that. I guess I never used those pins in some of my early tests on the board!

If I change the avrdude code to leave them set to inputs at the end then this issue will "go away" - until such time as someone wants to use the SPI bus, but then they'll need to remove the programming wires anyway.

I could enable a serial bootloader for the chips - and I did go down this route initially, but you still have to do the initial fuse-setting on the ATmegs (suppled totally blank), so you either needed an external programmer, or the ability to use the Pi as an ICSP host... Even using a serial programmer needs a GPIO line on the Pi to reset it anyway...

Do you (or anyone) think it's worthwhile going down the serial route? I have the bootloader .hex file (just needed minor changes to get the baud-rate calculation right for a 12MHz part)

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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 8:54 pm

I thought the process worked extremely well Gordon. What would be the advantages of the serial route?
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Re: Gertboard Assembly Thread

Tue Sep 25, 2012 9:35 pm

alexeames wrote:I thought the process worked extremely well Gordon. What would be the advantages of the serial route?
To be honest, I really don't know.

It would free up the SPI bus on the Pi - to use the ADC and DAC chips, but I suspect you'll not be using them while developing software on the ATmega anyway... I prefer the ICSP method as I can run minicom on the serial port and get serial access to the ATmega right away - the Arduino IDE is a little slow there on it Pi though...

I'll package up the bootloader at some point, so anyone who wants it can burn it into the ATmega via the ICSP interface if they want though...

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Re: Gertboard Assembly Thread

Thu Sep 27, 2012 8:27 pm

Curious if anyone has used Solder Paste for assembling these... Seems the surface mount stuff would be [strike]pretty easy[/strike] easier, if you did.
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Re: Gertboard Assembly Thread

Fri Sep 28, 2012 8:18 am

It honestly seems to me that I didn't need flux paste and this is the first time I've ever assembled anything like this.
I used to make such a mess with a soldering iron :oops: not sticking things together (except melted plastic insulation).
I watched a few soldering instruction videos, I realised I wasn't cleaning my Iron properly or ensuring the tip was tinned properly, and then everything magically stuck in the right places.
I also thought the cheapo Iron I had was rubbish because I bought one from Amazon to get the stand (life is not worth living if you mark the dining room table).
It turns out this one was much better than the more expensive cheapo rubbish I was using.

Or was it?
New tip. properly cleaned.

I have bought a cheapo soldering station now ( new toys), and I did use this for the assembly with lead solder. None of my teeth are loose yet ;)

The point is the hardest thing was getting over my fear that I was going to end up with homer Simpson type mess with the soldering Iron permanently stuck in the middle

As someone once said Soldering is easy
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Re: Gertboard Assembly Thread

Fri Sep 28, 2012 8:53 am

carlvk wrote:I
As someone once said Soldering is easy
It is easy and that's an excellent little article on soldering!

(I've been soldering for over 35 years though, so I guess it's easy for me to say "it's easy", but I did get som training from a good friend at the time!)

And a good soldering iron is going to be worth it's weight in some precious metal - trouble is, that's how much they cost now - I have an old Weller magnastat iron - and it was 2nd hand when I bought it 35 years ago and it's still going strong - but I thought it might be time for a new one - and eek! When I looked, a new Weller was in the £250+ price range, so maybe I'll keep my old one for a while yet...

I'm putting together a little project which will involve some soldering in the next 3-4 weeks and will make a little video of it all too, so that might be a bit of fun to look out for :-)

-Gordon
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Re: Gertboard Assembly Thread

Fri Sep 28, 2012 9:05 am

[email protected] wrote:(I've been soldering for over 35 years though, so I guess it's easy for me to say "it's easy", but I did get som training from a good friend at the time!)
I got my training terminating 88-pair cables on telephone-exchange frames. They didn't go anywhere - they were just for soldering practice, and when done to the instructor's satisfaction they were stripped, cleaned and soldered all over again...

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Re: Gertboard Assembly Thread

Fri Sep 28, 2012 10:35 am

alexeames wrote:I nearly messed up one of the chips first time round. One leg didn't go in properly and bent horribly. Was a booger to remove and then I had to straighten half the pins which got bent on removal. But it's alright now. :lol:
Inserting DIL ICs requires a bit of pre-work, in that you need to bend the pins so they are parallel. The amateur and dangerous way to do that is to put them down on their side on the bench and applying a firm downward pressure, tilt them until the chip is vertical. The danger is that you go too far, much too far if you slip. The professional solution is to buy a jig to do it, but it isn't cheap.

Once you have the leads parallel, insert the tips of one side into the socket and apply sideways force to bring the other side into alignment. It may require re-bending the leads until you have it right. Absolutely correct lead formation will require minimal force at this stage.

When the chip is in the socket sight down between the chip and the socket to detect any leads that have been bent underneath. It is not obvious looking at the lead from the outside.

To extract a chip apply a screwdriver or a PC PCI blanking plate under one end and lever it up. Then go to the other end and repeat. It is possible to work from only one end with experience, but probably not without.

IC leads that have been massively bent should be reformed with a pair of fine pliers and great care. They suffer hugely from metal fatigue; often breaking after only one bend and one reformation.

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Re: Gertboard Assembly Thread

Fri Sep 28, 2012 7:00 pm

Thanks Rurwin. I learnt a fair bit of that the hard way. :lol: Hopefully, thanks to your post, others will be able to avoid the fun and games I had. :D
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Re: Gertboard Assembly Thread

Sun Sep 30, 2012 8:32 pm

Just ordered a Deluxe Kit from Tandy.

Like every wet-behind-the-ears 18 year old trainee I passed through the Wiring School at the old ICL factory in Ashton back in 1983 - so was taught how to solder well, so in theory this should be a doddle (no SMT back then though).

I have just about kept my hand in over the years but this will be an interesting challenge, especially as I have the eyeballs and fingers of a 47 year old now... :roll:
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Re: Gertboard Assembly Thread

Sun Sep 30, 2012 8:37 pm

SN wrote:Just ordered a Deluxe Kit from Tandy.

Like every wet-behind-the-ears 18 year old trainee I passed through the Wiring School at the old ICL factory in Ashton back in 1983 - so was taught how to solder well, so in theory this should be a doddle (no SMT back then though).

I have just about kept my hand in over the years but this will be an interesting challenge, especially as I have the eyeballs and fingers of a 47 year old now... :roll:
I'm older... No problems here. But a good daylight lamp and a big magnifier is a boon.

-Gordon
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Re: Gertboard Assembly Thread

Sun Sep 30, 2012 11:07 pm

especially as I have the eyeballs and fingers of a 47 year old now.
Spring Chicken,
But a good daylight lamp and a big magnifier is a boon.
this is me using a head mounted magnifier.
http://www.flickr.com/photos/[email protected]/6305319953/

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