A Bit Big for a Bit, But

[chris101]

Hey Alex, @alexpikkert

I'm always open to suggestions, but I want to stay within a simple philosophy for this device. Like all littleBits modules, it's actions are easy to understand, and limited. First and foremost, this is an input module that knows the time, and can inject it into a littleBits circuit. But it also has some special features, because, ... I mean you just HAVE to, right?

Right now it has these main features:

• keeps the time accurately to the exact second,
• outputs analog time through three bitSnap connectors, hours, minutes and seconds. Analog time can be used to drive an analog or digital clock, engage with a circuit that needs to know the time, activate alarms, etc. It can even keep track of the music using the synth kit.),
• displays the current time with either an optional or built-in digital display,
• keep track of how long it has been since it's last setting, and resets automatically by contacting 'ulf' radio station WWVB. (The device can be configured to receive WWVB in Colorado, MSF in the UK, DCF77 in Germany, or two different frequencies of JJY in Japan. Right now, this would need to be set up at manufacture time, however a new chip and antenna from C-Max promises automatic transmitter switching. I have a CME 8000 chip in this device, but do not have the less than an inch long CMA-MF multi-frequency antenna... yet!) Here is a map of world-wide coverage:

• 'clown barf' display (flashing pink, yellow, green, blue and red super-bright LEDs) is a visualization of WWVB's various states. 'Clown barf' is displayed while the time is being set by WWVB. 'Clown barf' can be turned off with a toggle switch. The switch 'clicks' satisfactorily,
• time can be set on demand by momentarily pressing the 'set' button. When this happens, the device contacts WWVB, and then sets the clock to the received time.

I'm working on manual setting, alarms, and timers:

• if the 'set' button is held down, the time can be set using three pots, representing hours, minutes and seconds. When the button is released, the time continues from the new setting. NOTE: within a day, the device will contact WWVB, and the time will be reset to the Real Time, unless WWBV receiver has been turned off,
• alarms are set by selecting 'alarm' on the 'mode' switch and setting the time as described above. When the switch is returned to 'time' mode, the clock returns to normal operation, but the alarm time is remembered. When the alarm time happens, the 'clown barf' comes on, and HIGH LOW HIGH LOW pulses are sent to all three analog outputs,
• timers can be set on any of the outputs. In 'timer' mode, the time is set, and then counts down to zero. When zero is reached, the alarm sequence happens - barf, and pulses on the selected output.

Some hardware features:

• the WWVB radio, Arduino microcontroller, and Chronodot RTC can be turned 'off' by putting it into a low power sleep mode. While sleeping the device consumes less then 25 microamps,
• a lithium battery keeps the system alive, but in sleep mode, when it disconnected from power. Nothing is displayed, but the time, alarm progress, and timers continue to run. Nothing happens when they reach completion while in sleep mode,
• The device is sized so that it connects with the arduino bit and the wireless transmitter. The foot spacing and underside clearance is such that it fits onto a mounting board.
• A 5 female pin header brings the sda, scl, ground, +5v, and +3.3v out for connection to a user device. This can also be used to time-sync computers, TVs, and other digital equipment. I'd like to make this a better connector, but what is close and standard?

That's my current (and near-term) feature list. What else does it need?

[alexpikkert]

Hi Chris @chris101,
thanks for this nice detailed overview, now it is much easier to think about the design.....

[chris101]

Hey @blindbento!

I'm not even close to designing a double sided pcb for this! If it ever gets to that stage (and I am not counting on that happening) I will leave the design of the manufacturable device to professionals. I'm just building some devices (I've got 4 of them now) that I can work out some ideas.

The added display works nicely, but it's causing big problems for the radio. I moved the display device from the upper left of the board, above the antenna, to the lower right corner, and it still interfered:

The culprit may be the two 72mm leads that connect to the display module. When the display powered off, everything is fine, the radio receives the signal normally. As soon as the twi signal is turned on - even if the display is off, the interference starts. First thing I'm gonna try when I get a minute, is shorter leads. I would prefer to put the display back up above the antenna. But if that is not possible, I'll need to do some major re-designing of this device.

Another thing I need to do is change the way the output opamp and filter resistors/caps are wired up. Not for RFI, but for output impedance and current. You may notice I've removed some parts around the OPA4342.

[chris101]

Cool, thanks Alex! I look forward to your ideas.

[chris101]

It's been 6 months, so I want to give an update on this:

I have made several hardware mods, and have taken many of your suggestions into the design. The Atomic Clock has been running every day for over 5 months now, syncing the time as needed to keep perfect accuracy. It is always within one second of UTC.

Here it is, being used in my house as a radio time beacon:

[Eduardo_1448]

Hello can you help me? I'm looking for the op amp used in the littlebits, I saw that you bought it. I'm confused with so many options that appear to me when I type LMV321z on google, haha. I would also like to know what is the SOT353 that you mentioned. thank you !

[JackANDJude]

Hi @Eduardo_1448. I think the lmv321 chip only comes in smd packages. I searched Digikey, and sot353 is the package they had. I only tried etching and using smd parts this one messy time:

Instagram Judith Brisson on Instagram: “My first SMD circuit & etching = a messy success! 😅”

After that I decided to use thru hole op amp. I found a rail to rail thru hole dual op amp that Adafruit sells: TLV2462. I've used it a bunch and really like it. Here's the link: https://www.adafruit.com/product/808?gclid=EAIaIQobChMI8Mye-a6A4AIVSsDICh0xwwVQEAQYASABEgLS7_D_BwE

I hope that helps. What are you making, if you don't mind me asking?

[chris101]

Hi @Eduardo_1448, (and hello again @JackANDJude!)

According to the TI datasheet, Jude is correct when she says the LMV321 is only available as a surface mount device. The clock in this thread uses a 14 pin device, the OPA4342, which has four opamps on a single chip. I bought them on ebay. They fit the requirement to buffer one input and three outputs perfectly. Like the LMV321, the OPA chip is rail to rail (input and output), but the 321 can source much more current (60mA for the LMV321 vs 16mA for the OPA4342.) On the other hand, having four opamps in a single chip is useful when using bulky through hole chips.

There are other rail-to-rail opamps available to the hobbyist market as well. I too have used the TLV2426, for example in this 8 bit clock which needs only 2 amplifiers:

If you want exactly the characteristics of the LMV321, Sparkfun has a breakout board for the LMV358, which is the dual amp version of the LMV321.

Have fun in op-amp land!