Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: WYGIGS on September 09, 2015, 03:14:05 PM

Title: $50 robot power question
Post by: WYGIGS on September 09, 2015, 03:14:05 PM
Firstly, fantastic website! Thanks.

Background to my question:
I built the $50 robot with both 9V and AA batteries – worked first time – Brill!
I added Bluetooth (purchased cheap board) via uart. Worked first time! Brill!
Added Sharp IR distance sensor and transmitted distance via Bluetooth. Worked (second time – originally connected TR/TX direct rather than inverting). However, when IR and Bluetooth were working together, sometimes the communication was corrupt. I put this down to power issues. I duplicated the 9v battery, voltage regulator and capacitor, and connected the negative to the existing negative on the board. I use this to power the IR sensor. All seems OK, but I would be grateful of any comments?

Question…
I now have 3 battery sources to plug/unplug. I see all negatives are connected after the voltage regulation. Can I leave the positive as is, connect the negatives of the batteries together before voltage regulation, put in a single switch and then take the switched negative to the 2 voltage regulation circuits and servos, allowing me to leave the batteries connected? I was also thinking of adding some breakaway headers under the board for debugging without motors.
I realise a better battery source would be the best solution, but I’m learning!  :)

WYGIGS
Title: Re: $50 robot power question
Post by: mklrobo on September 10, 2015, 06:57:07 AM
 8) Awesome!
I would like to ask a question, where permissible. HOW did you program it? What software combinations,
where applicable? I appreciate your time and attention. Thanks!  ;D
Title: Re: $50 robot power question
Post by: cyberjeff on September 10, 2015, 07:26:14 AM

Question…
I now have 3 battery sources to plug/unplug. I see all negatives are connected after the voltage regulation. Can I leave the positive as is, connect the negatives of the batteries together before voltage regulation, put in a single switch and then take the switched negative to the 2 voltage regulation circuits and servos, allowing me to leave the batteries connected? I was also thinking of adding some breakaway headers under the board for debugging without motors.
I realise a better battery source would be the best solution, but I’m learning!  :)

WYGIGS

As long as there is absolutely no connection between the hot wires, that would work. But you need a better power supply for the IR and Bluetooth as they should be able to run off the same suply. With that you would have two supplies and you could use commonly available DPST (double pole single throw) or DPDT switches. 3PST switches are available but are neither common or cheap.

As far as the 5V regulators, assuming you are using 7805's, add a .1uF cap on the output, that will filter noise and "cross  talk".
Title: Re: $50 robot power question
Post by: WYGIGS on September 10, 2015, 02:56:32 PM
Thanks cyberjeff. I have now connected all my negatives from the 3 batteries to a common point, then into a single pole switch and from the other side of the switch out to the respective circuits. This worked. (see update below) I take your other points on board and will give them some more thought.


8) Awesome!
I would like to ask a question, where permissible. HOW did you program it? What software combinations,
where applicable? I appreciate your time and attention. Thanks!  ;D

From the main index of the $50 robot (http://www.societyofrobots.com/step_by_step_robot.shtml (http://www.societyofrobots.com/step_by_step_robot.shtml)), I simply followed the instructions under "Step 4 - Programming" for the initial robot, then added code from "Bonus! UART Tutorial Step-by-Step" and "Bonus! Rangefinder Upgrade" Beware of the implications of changing the clock speed in terms of delay and servo commands!
Title: Re: $50 robot power question
Post by: WYGIGS on September 11, 2015, 06:03:47 PM
Doh! My connecting the negatives worked until I connected servos and sensors - then it all went a little weird!  :-\
I'll try capacitors and reducing my power sources to 2.
Title: Re: $50 robot power question
Post by: mklrobo on September 12, 2015, 12:56:02 PM
 8) Cool! Thanks for the info! , +1 to WYGIGS!   8)
Title: Re: $50 robot power question
Post by: WYGIGS on September 14, 2015, 07:57:51 PM
As cyberjeff suggested, I now believe my original problem was noise from the IR Sensor corrupting the signal to the Bluetooth board. I've read lots of information on the IR sensor making noise on the power lines, and I'm beginning to understand. I've also read lots on decoupling capacitors, which I assume is cyberjeff's solution. I wanted to put all this information together to form my solution, which may have gone too far? I've drawn a schematic (not done this before so forgive me if it doesn't follow standards or is a little messy).

Could someone (with more experience than me) give the shematic a look over please. I need to buy parts before I breadboard it so would be grateful if mistakes could be pointed out before I place the order.

Thanks
Title: Re: $50 robot power question
Post by: cyberjeff on September 15, 2015, 04:12:40 AM
As cyberjeff suggested, I now believe my original problem was noise from the IR Sensor corrupting the signal to the Bluetooth board. I've read lots of information on the IR sensor making noise on the power lines, and I'm beginning to understand. I've also read lots on decoupling capacitors, which I assume is cyberjeff's solution. I wanted to put all this information together to form my solution, which may have gone too far? I've drawn a schematic (not done this before so forgive me if it doesn't follow standards or is a little messy).

Could someone (with more experience than me) give the shematic a look over please. I need to buy parts before I breadboard it so would be grateful if mistakes could be pointed out before I place the order.

Thanks

I don't see any issues, off hand.

Where and how  you ground are  important for noise  considerations. Ground returns should be direct and at a common point. Put your .1 uF bypass cap at that common point. The idea is that your various devices share the least amount of ground line.

When devices share a ground line, they also share any noise on that line.
Title: Re: $50 robot power question
Post by: ReidLage on October 27, 2015, 08:24:05 PM
As per my experience if there is absolutely no connection between the hot wires, that would work.
But you need a better power supply for the IR and Bluetooth as they should be able to run off the same suply.
As far as the 5V regulators, assuming you are using 7805's, add a .1uF cap on the output, that will filter noise and "cross  talk".

printed circuit boards (http://www.7pcbmanufacturing.com/printed-circuit-boards.php)