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Author Topic: 5 min meeting timer  (Read 750 times)

mogul

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5 min meeting timer
« on: September 22, 2016, 02:18:16 PM »
Where I work, CTO wanted to try something new. Project status meetings, time boxed to 5 min!

She asked if I could make her a timer for those meetings. 5 min fuses on firecrackers would be illegal here in Denmark, so I made an electronic contraption instead.

all-together.jpg
*all-together.jpg (48.3 kB . 702x768 - viewed 139 times)

Some time ago a colleague gave me a BBC Micro Bit board - he probably thought I someday would make something fun with it - Thanks Thilo!
BBC-Micro-Bit-Back.jpg
*BBC-Micro-Bit-Back.jpg (69.53 kB . 800x553 - viewed 137 times)
The BBC Micro Bit is a nifty little board, an uC, 25 LED's, a few buttons, and even more sensors on board. Good for this project.
BBC-Micro-Bit-Front.jpg
*BBC-Micro-Bit-Front.jpg (66.27 kB . 800x630 - viewed 137 times)
Turn it on, all 25 LED's light up. every 12'th second a random one goes out. When all is off, 5 min has passed and it beeps a buzzer. I coded it in a super child friendly scratch-a-like language.
5-min-meeting-timer-prog.png
*5-min-meeting-timer-prog.png (108.27 kB . 501x716 - viewed 135 times)

Source code:  *5-min-meeting-timer.jsz

Unfortunately the BBC Micro bit does not come with super power save modes, nor it has a buzzer on board. So I made it a control board with some electronics and the missing buzzer.
SupportBoard-Front.jpg
*SupportBoard-Front.jpg (60.21 kB . 800x764 - viewed 149 times)SupportBoard-Back.jpg
*SupportBoard-Back.jpg (71.81 kB . 798x768 - viewed 136 times)5-min-meeting-timer-sch.png
*5-min-meeting-timer-sch.png (38.25 kB . 1014x644 - viewed 139 times)
The two boards, and a battery box are bolted together

Here is a short video where I have modified the code to only have about a 500ms delay between each "tick"


« Last Edit: September 22, 2016, 02:45:13 PM by mogul »

bdk6

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Re: 5 min meeting timer
« Reply #1 on: September 22, 2016, 07:05:29 PM »
The firecracker would have been better, but this is really cool, too.

Impala

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Re: 5 min meeting timer
« Reply #2 on: September 22, 2016, 10:31:48 PM »
This thing reminds me of the episode of the Simpsons where the family gets shock therapy.  The scene when Maggie is pressing all the red buttons in between getting shocked herself!  -lol

ZeroMax

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Re: 5 min meeting timer
« Reply #3 on: June 12, 2017, 09:36:51 PM »
Ooh, yeah-If you could rig it with an electric flyswatter tennis racket zapper like Mehdi Sadaghdar's running belt and attach it to the meeting runner's nipples it would be a marketable product!
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maelh

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Re: 5 min meeting timer
« Reply #4 on: June 13, 2017, 09:26:06 AM »
Nice project.

Why do you need a filter capacitor for pin 0? And where is pin 2 on the schematic?

Did you really need the different types of transistors, or where they just what you had laying around?

I am learning electronics, maybe all of this is obvious.

mogul

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Re: 5 min meeting timer
« Reply #5 on: June 13, 2017, 04:26:54 PM »
Why do you need a filter capacitor for pin 0? And where is pin 2 on the schematic?

The cap on pin0 is for timing purpose, to make sure the ON pulse is long enough for the program to reach self hold.

pin2 is simply not used or connected.

Did you really need the different types of transistors, or where they just what you had laying around?

The 3 transistors function differently, but their particular models were what I had around. The power controller is a BJT PNP, the driver to the power controller is a N-chan MOSFET and finally the buzzer driver is a BJT NPN.

/mogul

maelh

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Re: 5 min meeting timer
« Reply #6 on: June 15, 2017, 11:22:22 PM »
Thanks for your explanation.
I thought about it a bit more, and I wonder why you need the 2N4403.
Couldn't you directly use the MOSFET to switch on the voltage regulator (as reaction to the push button).
And isn't the base of 2N4403 floating when the MOSFET is in high impedance mode (= open switch)?

Finally, why are those two blue components mounted vertically on an extra piece of veroboard?

mogul

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Re: 5 min meeting timer
« Reply #7 on: June 16, 2017, 04:55:08 AM »
I thought about it a bit more, and I wonder why you need the 2N4403.
Couldn't you directly use the MOSFET to switch on the voltage regulator (as reaction to the push button).

2N4403 is a PNP transistor. they can be "tuned on" by pulling the base down relative to emitter. Since I have the transistor on the positive supply line the only option is to pull down.

I could not have driven the 2N4403 directly from the microbit because that would pull base down when the microbit is powered of, which of course then would turn it on. The 2n7000 mosfet acts as an inverter here.
When base is low, drain is floating and no current flows through the base of the 2N4403.
When base is high, drain is pulled to down to source, conducting a current through the base of the 2N4403. which again make the 2N4403 open and power up the voltage controller.

And it would be the same with a mosfet in series with the voltage regulator feed.

And isn't the base of 2N4403 floating when the MOSFET is in high impedance mode (= open switch)?

It is floating, but it doesn't matter, a BJT transistor need a base current to open, not just a voltage as with the mosfets.

Finally, why are those two blue components mounted vertically on an extra piece of veroboard?

Ahh, I see i forgot those in the schematic. They are simple decoupling capacitors, probably 0.1uF or in that range.

 

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