Wireless Tumbler and Coaster

Continuing the theme of inductive projects I decided to make a wireless drinking tumbler and coaster combination to add a little sparkle to ones drink, but rather than using an off the shelf wireless phone charger to power the project I decided to make my own.

This would be truly wireless which unlike previous projects that were tied to a external power source would relying instead on batteries. After all you could be partaking of a drink in any number of locations that are indoor or outdoor and having to rely on an external power source would limit your flexibility of use.

Making use of inductively powered LED's in a specially modified drinking vessel negates the requirement for batteries that reside within the said vessel, meaning that the LED's can be fully sealed in the base and protecting from liquids whilst drinking or washing.

Requiring no on/off switches in any of the elements the function of the flashing illumination is controlled by the presence of the modified drinking vessel on the wireless coaster when not in place the circuit is in a low power state and when in place the circuit fully powers up.

Created specifically for the project a 3D printed case, PCB with associated electronics and hand wired coils.

Read on to find out how it works and was all put together.

Supplies

Surface Mounted LED's Red - Qty 4

Enamelled copper wire (ECW) 35AWG/0.15mm

Tinned copper wire 24AWG/0.58mm

Neodymiun Magnet 10mm (dia) x 5mm (H)

M3 x 8mm counter sink machine screws - Qty 4

M3 x 6mm pan head machine screws - Qty 4

Multistrand wire 28 AWG

Right angle pin headers - 4 to 13 subject to requirements.

Surface mounted components, package type 1206 (3216M)

Resistors 10R

Resistors 100R

Resistors 1K - Qty 2

Resistors 10k - Qty 2

Resistors 100K - Qty 2

Resistors 680K

Capacitors MLCC 10nF - Qty 3

Capacitors MLCC 100nF

Capacitors MLCC 1uF

Capacitors MLCC 47uF

Rectifier Diode 1N4001

MOSFET NType BS270 or BSS123

MOSFET Ntype FDT86113LZ

Timer TLC551 DIL or SMD - Qty 2

Battery CR2450 - Qty 2

Plastic Tumbler base diameter between 47mm & 96mm with ~7mm (base depression)

Filament PLA - Transparent.

Filament PLA - Silk Grey.

Filiment PLA - Black.

(Colours of filament subject to personal preference.)

Clear Lacquer

Clear Tape

Glue

Epoxy Resin for casting - Clear

May prove more cost effective to buy a range of values rather than individual values unless you already have them available. Some components may also have a MOL greater than the quantity specified in the component list.

Tools

3D Printer

Pliers

Wire cutters

Soldering Iron

Solder

Sanding paper

Needle files

Screw drivers

3mm drill bit

Know your tools and follow the recommended operational procedures and be sure to wear the appropriate PPE.

No affiliation to any of the suppliers used in this project, feel free to use your preferred suppliers and substitute the elements were appropriate to your own preference or subject to supply.

Links valid at the time of publication.

Step 1: Tumbler Selection

The plastic drinks tumbler requirements where that it should be transparent to enable the light effect to be visible from all angles. With a surface patternation to diffuse and reflect the light at many angles.

To keep it simpler the base should have a deep depression to house the coil and LED's. However, if one is not available selective milling can be carried out to create a recess for both the coil and LED's.

The base of the tumbler should easily fit within the confines of the coaster top area.

Step 2: 3D Design

The 3D design was created using BlocksCAD.

The two part coaster as far as possible would have the same dimensions as a typical square coaster with the exception of the height that needed to be greater to house the electronics, transmitter coil and batteries.

The coaster is designed so that all seams and screw holes are on the underside and the PCB, coil and batteries are mounted directly under the surface where the tumbler sits suspended off the bottom.

This is to minimise any contact with spills although the unit should not be immersed in liquid.

Coaster dimensions 96 (L) x 96 (W) x 16 (H) mm

The transmitter coil former is a two part construction with the two parts stuck together around which the wire will be wound.

Transmitter coil 47.4 (dia) x 2.5 (H) mm each half.

The receiver coil using a similar design to the transmitter coil former is also made of two parts stuck together this is attached to the lighting ring and is mounted in the base of a suitable transparent plastic tumbler which is then both held in place and protected from liquids by encapsulation in epoxy resin.

Receiver coil 26 (dia) x 2.5 (H) mm each half.

Lighting ring 47 (dia) x 3 (H) mm

The base of the coaster simply screws in place to hide and secure the contents.

Coaster base 92.8 (L) x 92.8 (W) x 2 (H) mm

Step 3: Printing

The elements are all printed using the same settings.

The coil former and lighting ring that will fit in the modified tumbler are printed using Transparent filament.

The coil former which sits within the coater is printed in black although any colour could have been used being it will not be seen in normal use.

The coaster is printed using Silk Grey.

Layer Height: 0.15mm

Infill Density: 100%

Base Adhesion: Skirt

No supports.

Even printed at 100% microscopic gaps can exist between layers, therefore applying a laquer or paint (clear or coloured), will make it easier to wipe clean and easier remove those glass ring marks.

Primarily designed for cool drinks (cold drinks develop condensation and hot drinks can deform plastic), apply a durable coating, wipe up condensation and spills regularly. Avoid exposure to hot drinks or failing this select a filament that has high temperature resistance.

Step 4: Post Processing

Some post processing in the form of filing and sanding may be required subject to print quality to remove strings or blobs that may be obscuring holes or result in uneven surfaces and edges.

Step 5: Circuit

Summary

The circuit consists of two TLC551 timers configured in Astable mode which drive the coil and whose operation is gated by the Hall effect switch.

The TLC551 timers were chosen as they are ideal for battery operation, being able to operate down to 1V at low current. Although in this case the limitation is due to the Hall sensors minimum operating voltage of 1.65V.

The Hall effect switch being used to enable or disable the oscillations by detection of the magnet housed in the base of the tumbler.

The resultant oscillations in the transmitter coil are inductively coupled to the receiving coil creating a voltage and subsequent current in the closed loop illuminating the LED's.

Function

The circuit is powered by two 3V CR2450 coin cells connected in series for 6V. These being chosen due to their relatively small size 24.5 mm (dia) x 5 mm (H), and high capacity for this form factor of ~615mA/H.

The Hall effect sensor is a digital omnipolar switch meaning to will respond in the same way to either magnet polarity with the output switching low in the presence of a magnetic field greater than the operating point (Bop) and switching high in the absence of a magnetic field lower than the release point (Brp). Where B refers to the magnetic flux density.

The sensor having a maximum supply voltage of 5.5V being powered by 6V necessitates a diode (Vf ~0.6V), be inserted in series with the supply line to comply with its requirements.

The output of the sensor is connected to the gate of the reset MOSFET whose drain is connected to the reset pin of the first timer. This MOSFET inverts the output of the sensor.

The reset pin of the timer is active low with a resistive pull to maintain it high when the MOSFET is switched off.

Therefore, when the tumbler is not on the coaster the reset pin of the timer is low and the output of the timer is also low.

The output of this first timer is connected to the reset of the second timer whose output is connected to the coil driving MOSFET.

When the tumbler is on the coaster the reset MOSET is switched off and the first timer is enabled as the reset pin is high.

The first timer is configured as a ~1Hz oscillator with the timing controlled by the CR network formed from 680kR and 1KR resistor with 1uF capacitor. Time period 950mS although actual values will vary due to component tolerances.

*See formulae below.

When the output pin of the timer is high the capacitor charges via the resistor until the voltage reaches 2/3 of the supply voltage this switches the output low which discharges the capacitor until the voltage reaches 1/3 of the supply voltage which switches the output high repeating the process.

The output of this timer gates the second timer which is configured as a ~12Khz oscillator.

Therefore a ~12kHz oscillation is active for ~477mS in each 950mS period.

The operation of this second timer works in a similar way to the first timer.. With charging occuring via two resistors and discharge via one resistor.

This results in an asymetrical mark space ratio due to the different charge/discharge paths.

Th (Time High) = 0.7*(R1 + R2)*C, Tl (Time Low) = 0.7*R2*C & Tt = Th + Tl = 0.7(R1 + (2*R2))*C

Th = 0.7*(10k+1k)*10nF = 77uS, Tl = 0.7*(10k + (2*1K))*10nF = 7uS

Frequency (f) = (1/0.7)*(R1 + (2*R2))*C = 1.44/(R1 + (2*R2))*C

f = 1.44(10k + (2*1k))*0.01uF = 12kHz

Duty Cycle(%) = Th/(Th+Tl)*100

77/(77+7) * 100 = 77/84 *100 = 91.7%

Note:

V = Vmax *(EXP(-t/RC)) therefore t = RC*LN(V/Vmax)

As the switching thresholds are between 1/3Vcc & 2/3Vcc then t = RC(LN(2/3)-LN(1/3)) = 0.693RC which is rounded up to 0.7RC

The output of the second timer is connected to a driver MOSEFT to which is connected the transmitter coil this being an inductor of 2.5mH. Knowing this and some other details we can calculate the voltage generated across the coil.

V = L*dI/dT = 2.5mH*(10mA/240nS) = 104V subject to the MOSFET performance.

In the standby mode (tumble not on the coaster), the supply current is ~100uA which based on a battery capacity of ~615mA/H gives a functioning time of 6150Hrs = ~8 months.

In operating mode (tumbler on the coaster), the supply current is 700uA max which gives a functional time of 29 days.

The functional times are subject to a minimum battery voltage of (Hall sensor Vcc min of 1.65V + Vf) = ~2.25V, although a realist minimum was ~2.5V.

However, the actual functional time will depend on how often and for how long the unit is used in addition to battery performance.

Step 6: PCB Design

The 2 layer PCB was designed using Eagle with a mixture of surface mount and through hole components, although SMD's predominate.

However, for flexibility the board will accomodate through hole timers on the front or surface mount timers on the back subject to requirements and/or component availability.

SMD and/or through hole MOSFET's and the Hall sensor are also catered for.

Mounting holes are part of the design to allow the PCB to be fixed under the transmitter in the coaster.

The PCB size is ~50 mm square.

Fabrication being carried out by OSH Park.

Step 7: Coil Assembly

The two coils are hand wound on the printed coil formers.

Starting with the transmitter.

First ensure that the surfaces to be glued are flat by rubbing on fine sandpaper and wipe clean with a cloth.

With a suitable adhesive stick the two halves together to create a reel.

Once the adhesive has dried and the two halves are firmly stuck together the coil can be wound.

Using 35AWG enamelled copper wire (ECW).

Create a free end of ~60mm of wire and wrap 200 turns of wire around the central former of the side element, trying to ensure that the windings are tight and evenly spaces. Due to hand wiring there will be some variation in the coil due to turns, wire spacing and overlapping but not enough to significantly effect operation.

Once complete secure the free end and cut the wire leaving 60mm and tape to the back of the side of the reel.

The free end lengths of 60mm are to allow easy manipulation during assembly and test and can be trimmed as required as the side pairs are fitted. Better at this stage for wires to be too long rather than too short.

Apply clear lacquer or varnish to the coil to hold the windings in place.

Next for the receiver.

Apply a similar process for the receiver but with 350 turns of 35AWG (ECW).

Step 8: Hall Sensor

The Hall sensor is attached remotely from the PCB on wires.

Take 2 x SIL 3pin headers and between them attach 3 x 60mm wires by soldering or wire wrapping.

Attach the sensor on one end.

Be sure to connect the correct pins 0 = Output, G = 0V and V = Supply.

The specific sensor used in this project has a push/pull output however, provision is made available to add a pull up resistor if an open drain output type such as the DVR5033 if used instead.

Additionally, the 1N4001 diode can be omitted if the sensor operates at 6V or greater.

Step 9: Board Assembly

Not strictly necessary but it may save unnecessary troubleshooting is to do a continuity check with a meter on any track containing vias in the event of an unexpected open circuit. Very rare but it does happen. If it does and in the absence of a through hole component feed a wire through the hole and solder to the pads on both sides. Not a problem for a double sided board but may not resolve the issue for a multilayer board.

As I will be hand soldering I normally mount all the passive components first and in the absence of the active components allows a check with a meter for opens, shorts or incorrect values at the pads were the active components will sit.

Regarding the timers (TLC551), if using the DIL package, mounting without sockets is recommended due to the addition height this will incurr preventing closure of the box.

If there are issues, find it or them and remedy the issue.

If there are no issues, I mount the active components ensuring they are correctly orientated.

If multipin SMD's such as IC's are mounted I would also do a continuity check between pins to eliminate shorts.

If there are issues, find it or them and remedy the issue.

If there are no issues, I would then mount any connectors.

Due to the tight space requirements right angle pin headers are recommended, although cut down straight pins could also be used in some areas.

Connect the Hall sensor to the PCB by the 3 pin header ensuring the correct orientation is maintained.

Prior to applying power I would check between the supply pins to ensure there are no shorts.

In some peoples eye's this may seem like overkill but a burned out board or component could turn out more costly than the time to check the build as you go, particularly if you few spares components which maybe costly or on long leadtimes.

Alternatively, you could just build it taking care to orientate the components correctly, place them in the right locations and carefully soldered, If it works all well and good, if not time for some fault finding.

However, at a cost, board test and assembly is an alternative offered by some PCB vendors if you wish to forgo this part of the process.

Step 10: Battery Power

The unit is powered by 2 x CR2450 coin cells which are housed in battery holders.

Connect the two holders together serially positive to negative with a wire to enable them to be mounted in opposite corners of the coaster.

Connect the remaining pins on the holders with wires identifying positive (red) and negative (black).

Attach the two battery holders in the coaster with adhesive or double sided stick pads.

Insert the batteries and with a DMM check that +6V is available at the two free ends.

Remove the batteries.

Solder the red wire to the 6V and the black wire to the 0V pin to the supply pins on the PCB.

Step 11: LED Ring

Open up the holes assigned for the LED's with a 3mm drill bit.

Using the lighting ring as a former, lay the 24AWG wire in one of the channels that passes through the four holes that will accommodate the LED's to form a complete circle and cut off the excess flush with the start. Remove the wire circle form the channel and solder the two ends together to close the circle.

Select a parallel channel that also passes through the four holes that will accommodate the LED's and repeat the same process.

Place the smaller of the two wire rings in the centre of the larger wire ring and solder one of the LED's across the two rings.

Lay the wire rings in the lighting ring and align the LED with one of the holes, mark the location of the three emply holes on the wire with a marker or needle file and remove from the lighting ring.

Solder the three remaining LED's on the wire ring ensuring that all the LED's are orientated the same way.

Taking the receiver coil, adjust the wire length as required and tin the free ends of the wire and solder one wire to each of the wire rings.

Prior to finalising the orientation of the receiver coil, power up the circuit and horizontally place the receiver coil on the transmitter coil the LED's will either illuminate brightly, not at all or very dimly. Ensure the orientation that gave the brightest illumination is the one that is maintained before fixing the receiver coil in place.

Ensure that the orientation of the transmitter coil is also maintained in relation to the receiver coil to maintain the brightest illumination. This can be achieved by marking the side of the reel to ensure its correctly orientated when fitted inside the coaster.

Fit the LED ring into the lighting ring, apply adhesive to the bottom of the receiver coil former and stick in the centre of the lighting ring such that the 10mm diameter holes in the centre align.

Apply adhesive to the 10mm (dia) x 5mm (H) magnet and insert into the centre of the receiver coil former, this will ensure that the two parts align.

Set aside until the adhesive has dried.

Step 12: Tumbler Modification

Determine the amount of resin required by measuring the amount of water that the cavity in the bottom of the tumbler holds. Then discard the water and dry the cavity.

Take a suitable two part clear casting epoxy resin and mix to match the quantity of water measured.

Pour part of the mix into the bottom of the tumbler.

Lay the LED ring in the centre of the cavity and pour the remainder of the resin to create a level base. Be careful not to apply too much resin which would create a bulge that would cause the tumbler to be unstable and require sanding.

Set aside until the resin has cured.

Step 13: Box the Circuit

Place the Hall sensor close to a magnet (ensuring the sensor is correctly orientated), and hold in place with tape.

Insert fresh batteries (ensuring to orientate them correctly).

Place one side of the transmitter coil horizontally close to the base of the modified coaster, if there is no illumination place the other side of the transmitter coil horizontally close to the base.

If there is no illumination in either orientation check the wiring for correct orientation, opens or shorts.

Ensure that the orientation of the transmitter coil is also maintained by marking the side of the reel to ensure its correctly orientated when fitted inside the coaster.

Apply adhesive to the side of the transmitter that will face the modified tumbler and press into the ring in the coaster, hold in place with tape.

Remove the magnet from the sensor and sick the sensor in the centre of the coaster identified by the square, apply adhesive in the square and insert the sensor, hold in place with tape.

Fix the PCB in place with 4 x M3 x 6mm dome head machine screws.

Put the bottom of the coaster in place and fix in place with 4 x M3 x 8mm counter sink screws.

Step 14: Operation

As the coaster is battery powered and maintains a low power standby state there is no requirement for an on/off switch.

Additionally, this minimises the number of areas open to the ingress of moisture.

In order to activate the unit simply place the modified tumbler in the centre of the coaster. With the tumbler in the centre maximum magnetic coupling is achieved and the LED's are at their brightest. However, off centre placement within the confines of the coaster will still illuminate the LED's just less brightly.

The magnet in the tumbler will be detected by the Hall effect switch and activate the circuit which in turn activates the LED's in the bottom of the tumbler via magnetic induction.

Removing the tumbler from the coaster will deactivate the LED's and put the coaster in a standby mode.

Wipe up spills or condensation regularly and do not immerse in water.

Step 15: Finally

Get yourself a drink, sit back relax and enjoy the experience.