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# Dot flippers

or "flip dotters" if you want. Let's just talk about flip-dot/flip-disc displays and projects using them :-)

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Seeing that my flip-dot outbreak has infected a few of my respected HAD fellows, I thought it was only fair to invite them here to discuss about these displays, exchange tips and links, and show off our progress using them :-)

Of course, we're not speaking about easy-to-arduinize system such as AlfaZeta's module. It's more fun to design the driver boards ourselves :-)

• ### Make a 14x24 matrix

Muth02/18/2021 at 13:25 1 comment

336 dots give more than 2500 components, I admit it start to be 'not-so-cheap'. Lets solder !

An aluminium plat will make a good support

I used jumpers to link the power and SPI lines between the boards.

Then I played a bit with ESP32 and socket communication over Wifi. I have then a program on a computer that sends video frames packets on this socket.

I've put the kicad and code here : https://github.com/pierre-muth/fast-flipdot

• ### A different driving strategy

Muth02/18/2021 at 10:57 1 comment

It's been quite a while I'm looking for displaying animation on a flipdot matrix. There is of course the impressive projects from AlfaZeta of Breakfast, but they are very expensive.

When I was looking closely to these matrices, I could guess they drive them by tiles, 8x8 or larger.

After playing a bit with raw dots, I observe that a charged capacitor of around 10uF at 16V, discharged directly into the dot's coil, is enough energy to make the dot flipping correctly. There is something to dig here, so I made a circuit with the coil in series with a capacitor, as shown below. One side is grounded. If you apply a voltage on the other side, the capacitor will charge, with a current flowing through the coil in one way. If you discharge the capacitor by grounding this same side, the current will flow the other way.

Now how to charge and discharge this circuit? With a CMOS, or complementary Mosfet for example. Lets try to simulate this concept in LTspice:

It seems to work, the green line is the current across the coil. Pulses in both directions are generated depending on which input is enabled.

One nice feature of this circuit is only the charge will consume energy, the way back is for free.

I choose a PIC with a handy SPI peripheral, plus two 8bit port. PIC16F15345, and start kiCad.

We can buy flipdots here on Hannio.org. They come in rows of 7 dots, probably because of 7x5 fonts. Using a 4 layer PCB, I manage to fit everything within the flipdot footprint.

A first test program gave me encouraging results:

• ### Desktop Clock

It's been a while (been doing other stuff) but I finalzed my driver board and libraries.  Clock has been working nicely for appx. 2 months now, as a pcb that just plugs into the Eurocard socket on the back of the board.

A few notes:

1) Current: who cares? I accidentally picked a driver that limits to 3A pulses, and the timing is really fast.  Just needed the right mix of caps and types to make it consistent.

2) I canned using GPS as a time source.  still using Wifi and NTP for ease.

3) I added an enclosure, just ordered the cnc routing.  something mid-century modern so my wife won't marie kondo it in 5 seconds - here's an exploded asm and a final asm pic:

PCB (didn't model the dots)

pcb with frame/enclosure for power supply

assembled pic

Shameless ripoff of this general bezel design from here:

All in all, not too bad.  if you want me to post pcb files etc lmk.

• ### Flipdot Driver board Experiments

OK So adding a few things for posterity:

Driver board works!  I have a dead IC channel (woops) but I can fix that.  Elimination of the cat from the workspace was really valuable!

1) The amount of time needed (I.E. Current) is actually pretty low.  not sure how to measure core saturation, if someone has any ideas, I'd love to hear them! I'd like to tune current pulse time to something pretty low.  Bottom line, average voltage is about 14v for 2ms,

2) Here's a scope trace of my the supply voltage at 15V.  This is adding ~3000uF worth of caps to the circuit!

The flip time is about 2ms as you can see from the current downswing to 13V (defined in my microcontroller as just a timer variable in ms, as sending the SPI commands is about ~30us) and it flips dots nicely - I bet it could go much lower in time, extra time sent to the coil actually seems counterproductive (overmagnetizing core? I dunno man)

3) It takes 5ms to charge the caps (the swing back to 15V) after a flip.  Reducing "on" time will help reduce how much capacitor charge time I need - any thoughts on what kind of components I can use to improve this?

• ### Progress in DIY flip dots!

Simon Merrett07/07/2017 at 11:17 9 comments

## Background

I'm a new member on this team but have been following the project for a while. My goal is purely for interest, rather than a specific project I need to make. I'd love to see these displays accessible for more people. So far I see three barriers to wider adoption that I think we can reduce:

1. Mechanical. To make these, you usually need to wrap a lot of wire coils. You need a decent low friction pivot and you need to make dots and frame elements repeatably and in quantity. When you scale all that up, making a usable array becomes hard work and not really worth the effort.
2. Electronic. These displays often need positive and negative voltages. They also need control circuitry that can handle these rails and this can result in H bridges, mosfets and optoisolators, not to mention multiple IOs from the controller IC for each dot or pixel. Multiply that by the pixel count of your array and the control electronics
3. Price. This is perhaps a consequence of the first two problems but often time is less critical to hobbyists and non-professionals, who are perhaps more sensitive to price.

So I've been trying to think of a way to improve in these three areas. The main idea I had was to use a micro servo (cheap, single 5V rail) to drive four dots or two dots (minimum IO pins per pixel) by rotating a notched wheel underneath the grid of dots. These notches would engage with a lever for each dot that would rotate 180° and magnetically couple to the disc of the dot itself. Like this: The lever pivots on the paperclip axel you can see in the bottom left. The motion of the "flip" and short settling oscillations are not conveyed well in this GIF but I found the action very pleasing and it produces a quiet fluttering sound which is a nice benefit.

The problem I was struggling to overcome with this arrangement was that to make this work with one servo creating all possible combinations for four dots, the 180° range of servo rotation would be have to divide into 16 to provide every possible permutation of four dots' settings (2^4) or divide into 4 (2^2) for two dots per servo. I couldn't get over this stumbling block as two dots per servo didn't really seem worth the effort to make each mechanism and four dots seemed too hard; the for a 25mm dot the radius of the notched wheel would be 50mm and resulted in around 4-5mm circumference between settings. That's not much distance to transition the lever mechanism from one position to the other and I put the idea on hold.

## Someone else's bright idea

A few days ago @Benchoff posted on the HAD blog about [sjm4306] using pager motors for a mechanical segment display (for a clock in this case). He encounters an issue of segments not being able to be arranged near each other without careful planning of the layout to ensure motors didn't end up being inserted and clashing. I immediately ordered some of the pager motors he used as I thought they could produce the magnet rotation that the lever of my first design provided.

Then I couldn't wait. I have some small pager motors already but they are the flat round type which are fully enclosed: I decided to see if I could break out access to the rotor and using small pliers prised off the cover (the sides and top surface in the picture above). I forgot to take a picture of the inside before I glued stuff onto the rotor but there is a cam-shaped rotor (eccentric mass to produce vibration) with two tiny copper wire coils mounted in it. On the underside of the rotor there is a commutator with around 6 plates (looked like more than 4). A pair of "brushes" or spring contacts supports the rotor from the stator and there's a tiny pin of an axel that keeps the rotor in place. There...

• ### Some more videos

Yann Guidon / YGDES06/05/2017 at 01:00 0 comments

Flip dots are really a fun, useful, easy, simple technology that can get more people interested in electronics and electronic data processing :-)

Now if anyone wanted to make a purely electromechanical TETRIS game ?....(I wish there was a way to read back the position of the flaps)

• ### Dots from Hannio

Yann Guidon / YGDES05/15/2017 at 22:51 5 comments

See the latest updates at the bottom :-)

The last log More on youtube introduced me to the tiny german webshop of https://hannio.org

I couldn't resist and bought two kinds items:

The pros:

• brand new, at least for the 1×7 modules, so unlike eBay you don't gamble...
• The 1×7 can be organised at will for any geometry, with a pretty good price.
• convenient payment with paypal
• fast delivery (5 days from order to delivery in France) for reasonable price

The cons:

• packaging... 1/4 of the 1×7 were damaged. One of the flaps is missing from one 16×24 and I don't know how to repair it (no spare for this very unusual part). I don't blame the sender because the carboard box seems to have been crushed and/or "inspected". The crush has damaged the 16×24's connectors...
• website only in German, not easy to contact the seller...

some of the 1×7 needed repair but that was easy.

Overall: very positive, good quality, good price/dot, I could easily repair most of the 10mm dots and the connectors of the 16×24 modules can be desoldered/replaced. And speaking German helped me again :-D

And since my last order, there is a new model : 16×28 module with controller board ! https://hannio.org/produkt/flipdot-modul-16x28/ Who wants to try it ?

Update 20170516 :

The coil resistance is measured at 19 Ohms. However some resistances have been measured as "infinite" and the thin, fragile wire was damaged during shipment. I'll have to check how many need repair and who many survive (anybody wants to help manually check 350 coils ?). The really broken ones will serve for surplus/replacement discs and will be cut in smaller lengths (because 7 is not a very convenient size to create 16 or 18-wide displays).

The resistance of 19 ohms is a bit higher than the 16.6 ohms of the other german panel I have so I expect slightly different flipping characteristics, but not far from 130mA/2V : 100mA@2V is better, indeed (but quite slow). However, higher current in needed to overcome the hysteresis of the factory-set dots : 2.5V/125mA is a good bet. It works well and fast at 3V. Direct drive is easy with a 3.3V power supply. Adding the diodes' drop (2×0.8V), the dots are suitable for matrices running with 5V.

I must still characterize the 16×24 array, which uses a single-coil structure...

June 20, 2017:

A new batch with mooooore flip dots ! I have accumulated about 1500 dots in original packaging. The shipping was a bit turbulent but less problems than before. The store owner will stuff the next packages with bubble wrap.

Another 16×24 array completes the others, so I might be able to also create a 24×32 or even 24×47 display (the last column has a missing flap).

And following my advice, the site is now available in english too ! https://hannio.org/en/

The stock of stripes is slowly running out so don't wait to get yours :-P

Yann Guidon / YGDES05/10/2017 at 02:56 2 comments

Dave Jones of EEVblog got some coiled dots :

And this video made me discover where to buy these 7×1 modules and 16×24 modules :

Now here is a very interesting store in Germany :

The 16×24 looks great !

They also look smaller than the usual display, which is great for graphics displays...

Has anybody else seen this model before ?

• ### The flipping point

Yann Guidon / YGDES12/21/2016 at 01:20 0 comments

So far I have received two kinds of flip-dot panels.

• A "PCB" type, where the coil is printed on the board. Very neat...
• A "wound" type, where the coil is made of enameled copper wound around the magnetic rod. Classic.

These two have different working points, as measured with a lab power supply:

• The PCB type starts to flip the dot when about 8V are applied to the coil. Add 0.7V (the unavoidable diode drop) and the LUMINATOR panel needs at leat 9V to operate. The nominal operating voltage is around 12V (compatible with my #YGREC16 - YG's 16bits Relay Electric Computer) but what's surprising is the operating current : the dot flips even down to maybe 20mA (the lab PSU goes in current-limit mode). I expected more... I suspect the PSU's output capacitors to store enough charge to create a current spike, so I'll have to test different configurations. Flipping power: less than 1/4W.
• The wound type (made in Germany) has a coil resistance of about 16.6 Ohms. The flipping current is around 130mA/2V, which means 3V or 3.3V with the diode. Flipping power: around 1/2W.

I'm amazed by the power efficiency of the LUMINATOR array. The printed coil is also more predictible and less subject to corrosion. OTOH the german displays are notably oxydized and several dots are damaged. I expected only one line (out of 19) to be unusable but mishandling might have occured and I can't get the 17 lines I wanted (16 data lines + parity, to spy on the memory).

Conclusion : if I give up on the extra parity line, the LUMINATOR is the best choice for my relay computer project. Thank you @Shaos for your precious help :-)

Now I have to examine the pulse characteristics...

• ### Just Blow

Yann Guidon / YGDES12/20/2016 at 21:51 0 comments

I received a couple of different boards from Germany and wanted to test them, without and driver. I'm tired and lazy so I just blew over it :-D

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## Discussions

manta103g wrote 03/12/2021 at 18:52 point

excellent
I am trying alike project employing DMD chip from DLP Video Projector

watch video of DMD chip and how it works

There is a problem, since I don't know how to dismantle DMD chip to get flashed directly with laser and get reflected pins projected on the wall.

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manta103g wrote 03/12/2021 at 18:52 point

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Ikepop15 wrote 08/27/2020 at 09:47 point

Hi there, I'm wondering if anyone could tell me what diameter the wire on the coil is and how many turns there are. I think that using coils are the way to go and to get the cost of making them down. If someone with a display could help me in the coil design that wound me amazing.

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Yann Guidon / YGDES wrote 10/09/2020 at 02:20 point

Some "coils" are made of PCB... so there is no "one solution fits all"

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Muth wrote 03/12/2018 at 08:21 point

I finally decided to use the original driving board of the old flip-dot bus sign I used. https://hackaday.io/project/47642-flip-dots-for-anti-matter-production-monitoring

Nice clock design, looking forward to the finished pictures !

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Yann Guidon / YGDES wrote 03/12/2018 at 11:20 point

Seriously !!!!!!!!!

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Muth wrote 03/12/2018 at 12:07 point

Thanks ;)

Not sure about HaD, I did not really hack the thing. At the opposite, I learnt a lot through your page!

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wuzandfuzz wrote 01/03/2018 at 04:17 point

@DJ: It's now down to 100us for a pulse, it's in the project chat.  it seems to work fine, no magic smoke, no hot drivers, but I am still a little scared.... any ideas how i can either measure the current pulse or assess if I am slowly nuking the driver chip?

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DJ wrote 01/02/2018 at 12:15 point

I'm with martin; stop limiting the current, and make  the pulses shorter. My dots pull 3A for half a ms, if I recall correctly. Also, for each column, you can set multiple dots off in one pulse, and multiple dots on in a different pulse, so you should only ever need 2 pulses to update an entire column. You'll *definitely* have to crank up the current limit for that though.

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wuzandfuzz wrote 12/22/2017 at 04:29 point

I bought a couple of boards recently, some time freed up.  I made a couple of PCB's based on NCV7708 to drive a 16x28 board - however I am running into a few problems.  It's pretty simple, just linking the driver outputs to the board for high low driving.

The dots flip, all of them!  However, they are extremely sluggish hooked up to my bench supply in voltage mode, 12V/1A max.  For some reason it always zeroes my supply!  This implies a sub-12ohm resistance which seems a little crazy.  It's worth noting that I did not populate an kind of smoothing caps on my board yet (there's no capacitance driving the circuit, just my test bench supply)

Any thoughts?

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Simon Merrett wrote 12/22/2017 at 07:32 point

Total guess but I think you are on to something with the capacitor thought. The coils could be acting as inductors which are slowing the build up of current and might account for the sluggish flips.

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wuzandfuzz wrote 12/23/2017 at 01:34 point

ok- some observations and improvements!  My cat tried to assassinate the board almost immediately after, but all the rows/columns are running.  It's a simple board, just 8x NCV7708's controlled over SPI to reverse current.

https://youtu.be/sHMtGhjDM2s

It's all running. But, this is with 3x270uF electrolytics and 4x100uF electrolytics in parallel!  Anyone have any thoughts if discharge rate is killing me?  This is a lot of capacitor.

I'll publish a scope trace later - but at a 20ms flip pulse, the capacitors are not recharging to voltage fast enough, with my bench supply current limited at 600mA. If I make the pulse shorter, the dots flip less reliably.  This makes me think a few things.

1) I need more charge to overcome inductive load - am I better off with Capacitance or Voltage, or both?

2) I'm starting to get nervous about how much amperage I am dumping in per coil.

3) I need to kill the inductive load faster - any thoughts here?

I also confirmed coil resistance - it's 1.2ohms (!!!!!!)  So a series resistor to limit current would just kill the voltage....

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Martin wrote 12/22/2017 at 09:37 point

Do you drive the dots in a matrix? Then you need to isolate them somehow, although it is complicated with diodes as they normally need bidirectional drive. But without diodes you are not only driving one dot but all of them. The wanted one with full current and the other with half current. I made this mistake long time ago with latching relays. Luckily they had two coils - like many flip dots have - and I could use diodes. One coil for set, the other for reset. You need 2 times the drive rows, but you do not need half bridges for each driver.

Of course you should use at least an electrolytic. The coils of flip dots normally have only very few windings., so very low inductance.

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wuzandfuzz wrote 12/23/2017 at 04:12 point

yes! each row is two pins.  you drive it one pin high or one pin low.

each column is one pin.  you drive it high OR low.

https://i.stack.imgur.com/oX0k3.png

I believe this is my situation.  It's working but I want to refresh the display faster, so either:

1) improve flip time or

2) lower current draw to drive more dots at the same time

Any thoughts? different capacitor type maybe to dump more charge? how can I overcome that initial inductive backforce?

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Martin wrote 12/23/2017 at 19:54 point

If you want to flip faster you need more power :-) Not lower current but higher, or better: The same current in a shorter time. To get more current in a shorter time you need more voltage. What counts is the peak current for flipping the magnetization of the core. The faster you reach it, the faster you can operate the display. I know flip dots which had a nominal voltage of 5V and a flip time of only a few ms. So your pulse is quite long.

You could stagger the flip pulses of a row to distribute the current spikes but its more complicated in the program. If you do not want to do this then use way more capacitance. You have only a little more than 1000µF. You should increase the capacitance so much that the voltage on the caps does not drop very much. Why not use 4700µF or 10000µF? And if your PSU goes into current limit then crank it up. The current through the coils should only be limited by the short duration of the pulse, not by a series resistor or by the PSU.

A higher operating voltage does NOT increase the inductive kickback by itself. This is only dependent of the current through the coil, Energy = LI²/2.

You should monitor the coil current with the oscilloscope. Of course you need quite a low current sense resistor, something like 0,05 or 0,1 Ohm as your load resistance is only 1,2 Ohms. Then you can optimize voltage and pulse length.

Why is the inductive kickback a problem at all? Does it damage your drivers?
If that's the case you could use clamping diodes from the Row_L drivers to VCC and from the Row_H drivers to GND, of course in a polarity, that they do not short out the supply. That also requires, that the row drivers a re switched off before the column drivers. You can also give the column drivers clamping diodes to VCC and GND. The coil current needs a way to go, when the switches turn off. Be aware, the lower the demagnetization voltage is, the longer the current takes to decay. But I think, the coils will demagnetize into the supply rail in this way, so that should be fast. Very similar to an H-bridge with the diodes of the FETs.

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Simon Merrett wrote 04/02/2017 at 22:18 point

Are there any attempts to make flip dot arrays in open source hw? It seems like a pcb coil is fairly achievable. A coil winding mechanism could be simple to make in order to scale up the classic approach. I've been toying with a quad arrangement of dots actuated with a micro servo - they cost in the \$1 order of magnitude in quantity and I have proven you can make a satisfying flip motion using a magnetic coupling. Unfortunately I haven't been able to make a mechanism that accommodates 2^4 states over a 180° servo throw, so I could only do a pair of dots per servo at the moment.

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Yann Guidon / YGDES wrote 04/02/2017 at 22:21 point

I have strictly NO idea...

If you do anything in this domain, keep us informed please ;-)

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Simon Merrett wrote 04/02/2017 at 22:25 point

Ok, will do, although I'm probably slightly overcommitted at the moment. Can't wait for updates/next log on this project!

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Martin wrote 12/22/2017 at 09:40 point

The key to the latching action of the flip dot is the ferromagnetic core and it's remanent magnetism after a short pulse. This can be difficult with a PCB coil.

Why do you want to control them mechanical with a servo, when you can do it electrical with some pulses? Are you building a Rube Goldberg machine?

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Simon Merrett wrote 12/22/2017 at 18:21 point

No, but the price of a micro servo split between four dots and the relative "potential" ease of assembly compared to custom tiny windings seemed attractive. I gave up on that approach after a short investigation and prototype. I'm now keen on the micro vibration motors approach.

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Dylan Brophy wrote 04/01/2017 at 21:28 point

I never knew this type of display existed! So cool!

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Yann Guidon / YGDES wrote 04/01/2017 at 22:12 point

Now you will look closely around you, you might notice a few, before they are all replaced with ugly shiny LEDs :-D

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