Cat Buzzer

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There where three cats living at Steamhead Maker Space in Shenzhen. This made for a lively show every now and then as each one woudl try to be king of the mat or box. I thought it might be fun to make a small randomized buzzer that would buzz for a second then go back to sleep for 30 to 60 minutes.

I forgot all about it until this morning. It didn't take long to whip up a demo circuit and PCB:

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The 20 pin STM32F042F6 MCU PCB includes both a magnetic and pizeo buzzer and will run from a small 750mA Hour LiPo battery. I will solder a TP4056 battery charger to the under side. This will help save space. If I do another version, I will migrate the 0805 resistors and capacitors down to 0603. I think I can shave at least 2mm x 5mm off the PCB dimensions. This will then allow me to add another three PCBs to the production panel

The 2020 Chinese New Year is just three days away, so I hope the order doesn't get lost in the exit stamped.

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Due to the virus issues, the PCB took a while to manufacture. I picked a green solder mask as this is the default colour and it normally will be manufactured in 2 days, vs. 4-7 days for a white solder mask:

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Underneath the PCB is a USB LiPo battery charger PCB. This is soldered onto my PCB using copper wire - you can see the square connection pads on the right hand side. While the board does work, the vibration motor only just turns over at the battery 3.2-3.8 voltage. While I am still waiting on the correct buzzer, the substitute buzzer faintly sounds.

I have had a re-think on the project and have instead moved to use a small 5V USB battery charger to power the board. I have removed the underside LiPo charger PCB as it's no longer needed. Next time I am in Shenzhen, I will test a number of small vibration motors to make sure they run ok at 3V range. I was hoping to put the PCB to sleep, but I think this will cause the 5V USB battery charger to drop the power supply as well, as there wont be enough current being drawn. As I write this, the next version is already on it's way to Busselton.

For people interested in a bit more info on the project, the top SWD 4 wire plug is the STM32 Software Programming/Debug port. The right hand side M1 plug is the vibration motor plug and the bottom plug is for the 3.2V Battery plug. You can just see the small micro USB plug poking out at the top right hand side (underneath the buzzer pad).

[Jubbp]

Nice work Paul

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The 5V version of the PCB arrived the other day. Systern had a go at applying the solder stencil/paste and placing the components onto the board:

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It works quite well:

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Current draw at 5V:
17mA idle
18mA LED on
140mA Vibrating Motor on
18mA Buzzer on

pretty happy with the way it's turned out. I trimmed the motor leads and it just vibrates in a small space between the PCB and housing. This helps amplify the sound. The housing worked first go and while it was design for the lid to be held in place using two 2mm x 12mm bolts screwing into corresponding heat set nuts, the lid fit well via friction. I have a short length of side lit 1.6mm diameter optical fibre acting as a light guide from the 0805 LED on the PCB below.

This is the last post for this project. The only thing left is to set some random awakening times, run the LED and motor and go back to sleep for another random length of time. Hard to blog about that.