Content in “srf05”

So it turns out making a lifelike drumming robot isn't as easy as you'd assume

TheCowGod — Thu, 17 Apr 2008 08:16:47 +0200

Well, I finished the construction, added the second drumstick up front, redid all of the circuitry on a PCB to eliminate the breadboard and clean things up, soldered up ribbon connectors instead of having loose wires everywhere, and glued down everything that was still hanging loose. So it's done, mechanically. Now I've turned attention to the coding.

The coding I had done for playing drums worked pretty well for music that I hardcoded by hand, but as I started thinking ahead to how I wanted him to be able to 'write' his own drum beats, I realized that I'd need something a little more programmatical and less music-oriented. So I took a page from real drum machines, and I redid my drumming routines to get rid of the explicit calls to play notes of varying lengths. Now, instead, I just divide a measure into 8 beats, and my drum patterns are 4 measures long, so that's 32 beats per pattern. I have 4 "instruments" (bass drum, two drumsticks, and a click from the speaker), so a pattern can be represented by an array of four 32-bit long integers. When I want to play the pattern, I just loop over each bit, and play the drum if it's a 1, or don't play the drum if it's a 0. I had to do some fun bitwise math to look at individual bits from each integer, but it works, and now I just need to come up with four integers and I've got a new pattern.

I came up with some quick and dirty code to let him come up with his own patterns -- each time I measure left/center/right distance with the sonar, I stick each of those measurements into bass drum, snare, and hi-hat. It shows promise -- they actually sound pretty musical. This whole 'coming up with his own patterns' thing will need some tweaking, to guide the patterns closer to musical and away from 'random banging', but it seems doable.

The part that I continue to have trouble with is the *&$king navigation. At first I thought I had found the problem when I realized that, since I had mounted my two drumsticks so far forward, my SRF05 was actually detecting those sticks most of the time when it looked left and right, so it was literally like he was wearing blinders. I cut the hot glue and re-glued the two motors angled farther back, so now that's not a problem anymore, but I still have trouble getting realistic numbers out of that sensor. Lots of times it will be like 8 inches away from a wall and pointing straight at it, and the sensor reports that the distances are something like (60 // 8 // 45) or (13 // 8 // 146) or things like that. The direction that is facing the wall head-on tends to work well, but the views to the sides seem to be completely unreliable. I added some debugging code to have it beep out the three distances through the speaker like the tracking devices in the movie Alien, with the pitch getting higher as the detected distance gets closer. That works really well for letting you know immediately how far away it thinks things are, at least relative to each other. And that has shown me that most of the time, it's getting totally incorrect numbers, which is why he can never manage to find anything to play drums on.

I know these sonar sensors have trouble when they're hitting a wall at an angle and things like that, so I'd expect little flaws every once in a while which wouldn't bother me, but this is pretty much just useless. I thought it might be my code for converting the pulses into measurements in inches, so I looked at the raw pulse numbers, but the problems are apparent there too, so I don't think it's a problem with my code. I almost feel like replacing the SRF05 with a Sharp IR sensor -- I get the impression that those are more accurate, though with a shorter range. But actually, the main reason I'm hesitant to do that is (embarassingly) an aesthetic one -- I think he looks a lot cuter with those big round SRF05 "eyes" rather than the tiny beady black eyes of a Sharp sensor :) Maybe I'll try using the PING sensor from my Harry The Discbot robot and see if there's any improvement -- maybe I just got a bad SRF05 or something. Frits, did you run into any problems like this with your sensor?

Dan

How to connect SRF05 to Picaxe 28 pin Projectboard

fritsl — Wed, 13 Feb 2008 17:55:09 +0100

If you are a newbee, you may only have learned that the Picaxe 28 pin Project Board has some inputs and outputs.. And you may have purchesed an SRF05 (that Picaxe refers to as SRF005), and you are trying to connect the darn thing.. without resoult?

Reason is likely to be that you are connecting the output from the Picaxe to the SRF05 through the darlington on the board.

The SRF05 needs (like many other things) a Pulse-signal, not just a "power on / off". The signal therefore must come directly from the Picaxe chip.

Luckely the board has little "hidden" holes for that kind of conections. (Blue wire, the signal in to the SRF05 directly from the chip). These holes, however, are not described, simply omitted in the manual for the board. So I wonder how a newbee should ever find out, personaly I burned a SRF05 or two in my frustrated attempts to get it right :)

If you follow the illustration above, you should be able to make the below code work just fine. You will know that the SRF05 is getting a pulse-signal when the little red LED on it´s back is flashing red.

****

symbol trig = 3 ‘ Define output pin for Trigger pulse
symbol echo = 6 ‘ Define input pin for Echo pulse
symbol range = w1 ‘ 16 bit word variable for range

main:
pulsout trig,2 ‘ produce 20uS trigger pulse (must be minimum of 10uS)
pulsin echo,1,range ‘ measures the range in 10uS steps
pause 10 ‘ recharge period after ranging completes
‘ now convert range to cm (divide by 5.8) or inches (divide by 14.8)
‘ as picaxe cannot use 5.8, multiply by 10 then divide by 58 instead
let range = range * 10 / 58 ‘ multiply by 10 then divide by 58
debug range ‘ display range via debug command
goto main ‘ and around forever

****

Notes:

I did not have a fresh SRF05, and so there are drilled extra holes and soldered pins on the one on the picture.

Be aware that if you also connect servo(s) to the same Picaxe chip, program execution may be bumpy with little iregular breaks when using things as the SFR05 that needs pulses. If it is important for you to have a steady program execution, or if a servo acts totally irrational, it sometimes helps to have a smal pause or turn off a servos pulse for a short time in the code:

"low 3" or "pause 10". Aparently there is no system, it is just trial and error with your particular setup.

These pages might have your interest: See what Robot Sees, 28 pin Project Board (AXE020), Picaxe for dummies

SRF05 Ultra Sonic Range finder

fritsl — Wed, 13 Feb 2008 16:12:32 +0100

IMHO the best way to have your robot measure distance to objects. Fast and accurate.

If you are using Picaxe, you may find this info useful: http://letsmakerobots.com/node/66

My second robot

fritsl — Thu, 07 Feb 2008 16:55:29 +0100

Primary image

What does it do?

Drives really fast, but poor, as both rear wheels turn the same, and no weight on front

This time I wanted a faster robot. No turning head, just some parts from old toy, mocked up, and getting much too high voltage!

It went completely beserk, but frankly; It was quite a poor robot, haha. (But fun)

Content in “srf05”

So it turns out making a lifelike drumming robot isn't as easy as you'd assume

How to connect SRF05 to Picaxe 28 pin Projectboard

SRF05 Ultra Sonic Range finder

My second robot

Primary image

What does it do?

Cost to build

Embedded video

Finished project

Number

Time to build

Type

URL to more information

Weight