# Choosing voltage regulator and battery for a compact RF remote control (transmitter)

I'm designing a remote control based on a TWS-DS-6 433.92MHz transmitter and I wanted it to be really compact and energy efficient.

I plan to have an ATtiny85 controlling the transmitter and use VitualWire software library to send data to the corresponding receiver (which is already up and running). I'll have the ATtiny85 sleep most of the time, only waking it up when the user presses one of four buttons on the control. I'll power the transmitter using a MCU digital output pin so I only turn the transmitter on when I need it.

The transmitter input voltage is 5V (Edit: correct range is 1.5 to 12V). The controller will have 4 push buttons, each of which will send a different command to the receiver. I plan on mounting the transmitter boards on one of those small remote garage door opener cases like the one below.

Case dimensions in this case are 18x40x67 (mm).

I have a version of the transmitter working on a Arduino Uno with an ATmega328 (not on deep sleep mode yet) on a protoboard.

Could someone please help me choose a low quiescent current 5V regulator and battery for my remote control?

Also, does anyone see any flaws or room for improvement on my design?

• What current consumption are you envisaging? – Andy aka Oct 25 '13 at 16:36
• @Andyaka Humm... it's hard to tell right now. I think I can get the uC to use less than 5mA when awake and uAs when sleeping. The tranmitter will take a few mA as well when transmitting, but I'm not sure how much. It should be off during sleep mode. I'll make some tests at home and report back here. Then I need to figure out how much current the regulator will take, hopefully in the uA range when the uC is sleeping. – Ricardo Oct 25 '13 at 16:46
• @Andyaka Here you go, TWS-DS-6 datasheet says Current : 23mA(5V); 40mA(9V); 53mA(12V). – Ricardo Oct 25 '13 at 17:13
• erm... You've accepted an answer so no need to provide more info theoretically unless you believe the question has not been properly answered. – Andy aka Oct 25 '13 at 17:18
• @Andyaka Well, there's significant doubt as to whether the CR2032 battery will power the transmitter, even with the low leakage capacitor. If you have a better suggestion, I would love to read about it. – Ricardo Oct 25 '13 at 17:21

TWS-DS-6:

Supply Voltage : 1.5~ 12 V

ATtiny85:

• Operating Voltage
– 1.8 - 5.5V for ATtiny25V/45V/85V
– 2.7 - 5.5V for ATtiny25/45/85

I wouldn't bother with a regulator. Assuming the transmitter doesn't use a lot of power, I'd use a CR2025 or CR2032 directly.

• Right, the transmitter is 1.5~12V. The receiver is 5V. My mistake. Well, things got much easier now. I really wanted to go with a CR2032. I'll just watch for the range as it is influenced by the supply voltage. – Ricardo Oct 25 '13 at 16:54
• The TWS-DS-6 datasheet also says Current : 23mA(5V); 40mA(9V); 53mA(12V). Unfortunately it doesn't say anything about 3V. But if it is around 10 to 20mA, that would be too much for a CR2032, wouldn't it? – Ricardo Oct 25 '13 at 17:04
• @Ricardo: Yes. But not for a low-leakage SMD polarized cap. Better size it for a few presses though. Although to be fair, I have been able to pull 10-12mA from a CR2032 before. – Ignacio Vazquez-Abrams Oct 25 '13 at 17:05
• How would that work? I would put the cap in the circuit so it charges and stores energy for when the button is pressed, when it would power the circuit and provide the few mA that the circuit need and that the battery cannot supply directly. Is that it? Do you have any examples of this technique in practice? – Ricardo Oct 25 '13 at 17:09
• @Ricardo: The ATmega8HVA et alia battery management MCUs use a cap to store enough power to run the MCU during overcurrent situations, when the battery voltage drops too low to power the regulator. – Ignacio Vazquez-Abrams Oct 25 '13 at 17:16