Remote Controlled Lanterns

 

Context

This year's spring production of Lucy Kirkwood's The Children features a sunset that gradually gets darker as day turns to night. The premise being that due to a local power station disaster power is limited to late in the evenings so lanterns are lit once it begins to get dark until the power switches back on.

Switching on was easy enough, as actors were handling them when they needed to illuminate. The complicated part was switching off because they were only supposed to turn off during the final blackout.

As the lanterns are moved around the stage throughout the show, it made sense to look into a wireless DMX solution.

City Theatrical's Show Baby 6 wireless DMX was chosen because it had been used in the past with minimal issues. The receiver has a decent, credit-card sized, low profile to hide in small places. 

QolorFlex receiver in the base

Original Lantern Limitations

Original product

The lanterns chosen consisted of a white metal frame with glass edging that housed 15 bright warm white LEDS. An adjustable switch controlled brightness with power supplied by 4 x AA batteries.

The first problem to present itself was that the LEDs require 6V to run, but the minimum input voltage for the Show Baby receiver was 7.5V.

Power

A power solution would need to be found that could supply 2 different voltages and also be small enough to fit inside the base of the lantern. 

Below is a diagram of the solution we came up with. Starting with a 9V battery to power the receiver, we then use a linear voltage regulator to jump down to 5V for the LEDs. (It was decided safe to assume that the LEDs would power just fine with 5V.)

Wiring sketch

9V supplies power to the receiver allowing it to listen out for a signal from the transmitter. From one of the 4 outputs our circuit extends into the input a LM7805 voltage regulator. Regulated 5V then flows into the lantern LEDs. Smoothing capacitors have been placed either side of the regulator as per the datasheet recommendations.

Powering this circuit up resulted in success. Unfortunately due to the limitations of 9V batteries the input voltage to the receiver had dropped to below 7.5V after 20 minutes with complete failure after an hour. This would not be long enough to get through the show so high capacity batteries were looked into.

Our senior LX had a bunch of 18650 batteries that were no longer needed so we decided to try these out. At 3.7V each they could easily provide enough voltage when used in a battery holder that can take 3 at a time.

18650's in charging station

Success! In practice they only drop by 25% after an entire show with roughly a 50/50 ratio of being on standby and lighting the LEDs. 

Final arrangement

Finishing Touches

Some light frosting was added to the glass to hide the LEDs and white paint lids were added to the bottom to extend the base. They are held on with a combination of black tack and white LX tape. The dimmer switch was not needed and so removed and the remaining hole is used to poke the receiver antenna out of.

Lantern with antenna visible

Result

The lanterns have direct line of sight with the transmitter located in the auditorium just off to the left of this image and are turned on simultaneously with visual cues from the actors. The improved battery would likely reliably last 2 shows before being changed, and leaving them on standby has shown results of up to 18 hours.

The battery holders are quite stiff and care needs to be taken to ensure that the batteries are making good connection with the contacts. Its seems the springs aren't overly "springy" but fortunately it's easy to spot as the lantern won't power without this check.

The frosting hides the LED source well and they continue to stay lit when taken off stage briefly. The intended effect is produced effectively and the final moments of the show looks great when everything turns off in unison.