Tic Tac Tunes - Now with Tic Tac Beat Box

Step 5 Circuit Diagram

As space is at a premium here, I'm using a small 6V battery and dropping the voltage down by 1.2V to 4.8V with the diodes D1 and D2. The PicAxe chip is happy up to 5V so this is fine.

R1 and R2 are required to allow this to be programmed in-circuit and to re-program I plug in the USB / serial programming lead to the 3.5mm socket under the box lid.

The 0.1uF decoupling capacitor is good practice with any circuit. It absorbs the voltage transients when transistors within the ICs switch. Without these, digital circuits can behave very strangely.

R3 is to pull the input to ground when the probe is not touching the track, otherwise it floats and generates all sorts of spurious noises. The solder blob on the track is to the positive rail to give a definite level for the control.

I've used a wide angle red LED but any LED will do. Drop R5 to 150R or so if using blue or white. There's not a lot of LED activity so as to keep the current consumption down.

Current consumption is around 1mA when active and drops to 200uA when in sleep mode, so the battery should last a fair while.

^{I used ExpressSCH to draw the schematics, and PDF Redirect to save to a PDF file. Both free.}

Comments

[futureventions]

With the peizo sounder, what colour wire attaches to the Picaxe?

[AndyGadget]

 
It doesn't matter - Connect the piezo either way around. 

That only comes into play when you're using two or more speakers :-  If you connect them different ways around then one is 'pushing' the air in one direction while the other is pushing in the other, so the pressure waves (sound) from each would tend to cancel out to some degree.
This is very noticeable with stereo loudspeakers if you connect them to the amplifier with one reversed. (It's called 'phase reversal'.)

[jeff-o]

Would the circuit run on just 3 volts?

[AndyGadget]

3V is the absolute minimum operating voltage for the 08m but you couldn't program it at this voltage. There is a 1.8 to 3.3V operating variant of the more advanced PicAxe X2 chips, but not the 08m. The centre frequency of the sounder is 4.2 KHz, but I chose it for the flat profile rather than the electrical characteristics. Whatever you use it will sound pretty tiny in that box.

[jeff-o]

Ah, I see. So, I could temporarily hook up 5V during programming, and the rest of the time run it from a 3V lithium cell?

[AndyGadget]

Yep, that should work. Make sure you disconnect the 3v while 5v is connected otherwise the battery will overheat!

[jeff-o]

Naturally. ;) I suppose I'd also have to change the resistor for the LED, but that's a trivial change. Oh, and I'll have to make sure the piezo is happy running on 3V as well.

[AndyGadget]

Good point. A blue or white might struggle because of the Vf. Red would be best. Piezo should be OK, just quieter.