To Webbot: Please re-look you PCB design of 50$ robot MCU

[huevon]

Hi
No fence Webbot, as I said before you have done pretty good work but after having really hard time debugging my board I started building a new one and noticed that the filtering capacitor C1 is placed wrong (please see attachments). C1 is supposed to smooten the output voltage after the voltage regulator. So should be connected between the output pin of the voltage regulator and ground. Looking at your design is connected between +6V (unregulated pins) and GND (ground) practicaly filters nothing! After I completed the second board I had same issues like the previous one (http://www.societyofrobots.com/robotforum/index.php?topic=11082.0). The solution for myself was easy, just drilled two holes as shown in the picture below and moved C1 to its new place. That was possible because the switch I am using is much skinnier than designed (http://www.maplin.co.uk/Module.aspx?ModuleNo=2480) it fited perfectly. Both programmers reconised it and are able to program it. Haven't tested it further.

Of course there might be a bloody good reason for that cap to be there, but please share your knowledge with us because I worked really hard and I am not that clever at all  

[airman00]

Usually there are capacitors on both sides of a 7805. Like here

[Webbot]

I have amended the tutorial and there are now two capacitors.

Still slightly strange you have had problems as my one works okay and I still use it quite a lot!! Isn't that always the way.

[huevon]

I have amended the tutorial and there are now two capacitors.

Big thanks on behalf of all noobs I represent  

Still slightly strange you have had problems as my one works okay and I still use it quite a lot!! Isn't that always the way.

My theory is I am using a bit dodgy voltage regulators (http://www.maplin.co.uk/Module.aspx?ModuleNo=46321) hence the problem mega328P wasn't powered properly.

[Soeren]

Hi,

In this post is another stab at both schematic and PCB, if that would help any.

[huevon]

In this post is another stab at both schematic and PCB, if that would help any.

Hi Soeren,

I was also thinking about smaller version of this MCU and all I can say is thanks very much, you have done all the job instead. But what really intrigued me was that SEPIC supply you mentioned. As soon as I finish $50 MCU v.webbot will do some research how those SEPIC work. And yeah, I want to join your project 

[flubber_butt_2001]

I'm getting a problem with the MCU also. When I try to connect the Atmega8 to AVR Studio the programmer (AVR MKII) has one green light and one red light. Do you think if I add this new capacitor it will be better?

[Webbot]

The capacitor wont make any difference - its only there for smoothing out current surges like once you've got devices connected

As said previously: the design is fine and works for me. (Always the way).

Your green and red LEDs mean that its not detecting the ATMega. Have you tried plugging the programmer in the other way around?

[flubber_butt_2001]

I tried plugging it the other way around but i get an error also. Says something along the lines of not enough power. I've been matching the line so that the ground pin goes with the ground female connector though.

[Webbot]

may be worth reading http://www.societyofrobots.com/member_tutorials/node/290 you must have some wires mixed or some bad connections.
With your meter do you see 5v on the power pin of the programming header?

[huevon]

I completed my new bord $50 MCU v.webbot_1.0 and works fine as far I can test it. I programmed the flash with servo_hold.hex but servos didn't moved as expected however I am able to blink the led. About servos I have, they are very dodgy £2 each of e-bay, so I don't trust them. Just bought 4 futaba3003 hope they come soon to see what will happen.  

You can see my baby in the attachments. You will notice there are pins on the old place of C1, there were hols anyway so I decidet to have an aditional unregulated power outlet. I am also using two caps connected paralel to have double capacity. I am not realy sure does the 200uF improve things but with these fake voltage regulators I have, became paranoic.

[Webbot]

Good job.
I'll keep my fingers crossed for you.

[flubber_butt_2001]

I've checked all the connections on the board and they seem to be correct and there are no shorts. I've also checked the voltage its receiving, which is 5V. I'm still getting the red status light inside the programmer so I'm not sure what to do now.

[huevon]

I've checked all the connections on the board and they seem to be correct and there are no shorts. I've also checked the voltage its receiving, which is 5V. I'm still getting the red status light inside the programmer so I'm not sure what to do now.

Hi
I know the feeling but don't give up so easy, especially when everybody else had made it to work 

OK
I assume you have done the MCU following webbots tutorial. This is PCB so isn't that easy to mess up connection so we assume connections are fine.
Red light means your board is not powered, and that is 100% sure! AVR MK2 measures the voltage same like a voltmeter, if RED, means NO POWER! I just made an experiment with mine especially for you I powered my MCU with 4.5V and even 3V and red light changes to green. So I am sure you don't get the correct voltages. If you power is unstable as mine was, then you will get blinking orange.
Now take the board where is a sunlight and take your time to have a good look for something obvious (inverted AVR in the socket, inverted programmer header, inverted polarity of the power supply, is your battery pluged in to the correct socket for example not in the motors/servos unregulated circuit). Does your board look like mine, use my attached pictures to try to discover diferences.
Do that, tell us what did you find, and then will continue with the debugging. An why not send us some close pictures of your boad top and bottom, and how it looks when connected and powered also may help.

[huevon]

Does anybody know how to change the name of this topic. This thread doesn't concern Webbot any more. When I started it I just wanted to report a flaw

[santiago]

webbot, can you you provide a link to the PCB design of #50 robot MCU that you  have amended(for the one that there are now two capacitors).
I need the gerber file. I think that's what is called. Besides the schematic.

Thanks for all you do.

[huevon]

Hi Santiago
here is attached .zip which I downloaded recently wrom Webbots tutorial http://www.societyofrobots.com/member_tutorials/node/190
You can download it from there as well.
Good luck with your project

[santiago]

Thanks, huevon

[santiago]

huevon is this image already in mirror mode ? or do I have to set my laser printer to mirror print & scalling fit to paper size (I think this means fit to scale).

[huevon]

huevon is this image already in mirror mode ? or do I have to set my laser printer to mirror print & scalling fit to paper size (I think this means fit to scale).

It is a mirror image, you can judge by the small text in the bottom right corner.
Print it as you see it, make sure there is no scaling.
Webbot has included in the archive a .pdf of the top view, so there are no mistakes.
iron, etch, solder, done 

[santiago]

Cool, Okay.
Thanks

[flubber_butt_2001]

I finally figured it out! Flipped the atmega8 backwards... I thought I built the IC circuit backwards accidently, so I made sure to mark the right side but the right side was infact the wrong side  ! Good thing you posted a picture of yours or else I would have been going crazy for a bit lol

[flubber_butt_2001]

Also for anyone who's curious, I only used the one capacitor also and it worked.

[huevon]

Congratulations 

[santiago]

huevon, what size of drill bits do we use for this circuit? I have a 1/16 but that might be to big for the smallest holes.

Thanks for your reply.

[santiago]

what was the drill bit size?

[huevon]

I am not familiar with imperial units but in metric I used 1mm for terminal pins and 0.8mm for IC Socket, resistors, etc
But of course that is me, you can find many different recommendations if you google it

[santiago]

I don't want to use the switch that is shown on the pics. I just want to simply use a of on switch. Thus, what do I have to do to make this possible.

By the way, with the DPDT switch that is shown by default is it possible to have regulated and unregulated on at the same time?

Thanks for yas help

[SmAsH]

With the switch shown, you can turn on regulated and unregulated, To eliminate the switch just short across the top holes and bottom holes of the switch separately.