Transmitters: PS & USB & UI

[NZ0I]

Having given some thought to the power supply design for the dual-band transmitter, this is what seems to make sense:

BUCK CONVERTER FOR TRANSMIT POWER CONTROL

To allow the processor to have great control over the transmitter output power, a high-efficiency buck regulator can be used to set the collector/drain bias voltage of the final output power amplifiers. Using I2C the processor will be able to adjust the output power from ~100 mW up to ~1.5 W. This will allow minimum transmitter power to be used as appropriate for the transmitter activity, and it will also allow the processor to throttle back the power to protect the final amplifiers in high-SWR conditions (e.g., someone forgot to connect the antenna!)

12V BATTERY SUPPORT OR BOOST CONVERTER

The transmitter will be able to work directly off of any 12V-14V power source capable of providing 1A or more of current, such as an SLA battery. Alternatively, many other power sources will also be supported by the optional inclusion of a high-efficiency boost regulator. The boost regulator will be able to transform any 3V to 10V power source capable of providing ~10W of power, to +12V to power the transmitter. That includes suitable single-cell LiPo batteries.

CHARGING SUPPORT FOR LIPO BATTERY

To support single-cell LiPo batteries, the transmitter will include the same USB charging and protection support, the same as the receiver. A back-of-the-envelope calculation suggests that a transmitter should run for more than 5 hours at full transmit power (10% duty cycle) from a fully-charged 2200 mAH LiPo battery. So I think that LiPo batteries are a viable option for these transmitters.

And some thoughts regarding how the user communicates with the transmitter...

USER INTERFACE

The transmitter design currently lacks any dedicated user interface. It has no buttons or LEDs (yet). The idea is to have it plug into a Control Head for programming. The Control Head has a 2-row x 20-character LCD display, four push buttons, and a rotary encoder. When a transmitter is plugged into a Control Head, the user will be able to use menus to program the call sign and other transmitter configuration data, and synchronize the transmitter's real-time clock to the Control Head's clock. Once programmed, the transmitter would retain the data in EEPROM. The settings could be confirmed by reconnecting a Control Head, and also the transmitter might be programmed to send out its configuration in Morse code (one external pushbutton might be needed to trigger this behavior) with the final amplifier disabled - so a nearby handheld receiver could be used to receive the communication. 

A simpler-to-use user interface approach would be to have the transmitter interface with a laptop computer, or perhaps a cell phone. Since laptops and cellphones are so ubiquitous, there would be little additional cost involved for most users. A straightforward approach would be to connect a standard USB-to-microUSB cable between a laptop and the transmitter (the same type of cable and the same jack that would be used to charge its LiPo battery). The laptop (or desktop) would then communicate directly with the transmitter's processor via a USB-to-UART converter. Windows, OS X or Linux should all have standard drivers that would allow them to recognize the serial connection. A simple/standard terminal communication program running on the PC/Mac/Linux machine is all that would be needed to communication with a connected transmitter using a command/response protocol. The following chips are examples of what would need to be added to the transmitter: http://www.digikey.com/products/en?keywords=768-1007-1-ND, or http://www.digikey.com/products/en?keywords=768-1129-2-ND. Those devices are being used in products like this one from Sparkfun: https://www.sparkfun.com/products/13263

A similar interface could be used with a cellphone running Android or iOS. A WiFi TCP-to-UART converter (like this one http://pignology.net/piglet/) could be used to interface the transmitter with any cellphone running an appropriate app. A single wireless converter external to the transmitter could be shared amongst many transmitters.

The external serial/USB interface should also support transmitter firmware updates, and for that reason the same support should be added to the dual-band receiver as well. More fun things to explore.

 

[Gerald Boyd]

That's an interesting idea. Sounds like it should work.

Sent from my iPad

On Mar 3, 2017, at 3:06 PM, NZ0I <charles....@gmail.com> wrote:

Having given some thought to the power supply design for the dual-band transmitter, this is what seems to make sense:

BUCK CONVERTER FOR TRANSMIT POWER CONTROL

To allow the processor to have great control over the transmitter output power, a high-efficiency buck regulator can be used to set the collector/drain bias voltage of the final output power amplifiers. Using I2C the processor will be able to adjust the output power from ~100 mW up to ~1.5 W. This will not only allow minimum transmitter power to be used as appropriate for the transmitter activity, it will also allow the processor to throttle back the power to protect the final amplifiers in high-SWR conditions (e.g., someone forgot to connect the antenna!)

12V BATTERY SUPPORT OR BOOST CONVERTER

The transmitter will be able to work directly off of any 12V-14V power source capable of providing 1A or more of current, such as an SLA battery. Alternatively, many other power sources will also be supported by the optional inclusion of a high-efficiency boost regulator. The boost regulator will be able to transform any 3V to 10V power source capable of providing ~10W of power, to +12V to power the transmitter. That includes suitable single-cell LiPo batteries.

CHARGING SUPPORT FOR LIPO BATTERY

To support single-cell LiPo batteries, the transmitter will include the same USB charging and protection support, the same as the receiver. A back-of-the-envelope calculation suggests that a transmitter should run for more than 5 hours at full transmit power (10% duty cycle) from a fully-charged 2200 mAH LiPo battery. So I think that LiPo batteries are a viable option for these transmitters.

And some thoughts regarding how the user communicates with the transmitter...

USER INTERFACE

The transmitter design currently lacks any dedicated user interface. It has no buttons or LEDs (yet). The idea is to have it plug into a Control Head for programming. The Control Head has a 2-row x 20-character LCD display, four push buttons, and a rotary encoder. When a transmitter is plugged into a Control Head, the user will be able to use menus to program the call sign and other transmitter configuration data, and synchronize the transmitter's real-time clock to the Control Head's clock. Once programmed, the transmitter would retain the data in EEPROM. The settings could be confirmed by reconnecting a Control Head, and also the transmitter might be programmed to send out its configuration in Morse code (one external pushbutton might be needed to trigger this behavior) with the final amplifier disabled - so a nearby handheld receiver could be used to receive the communication. 

A simpler-to-use user interface approach would be to have the transmitter interface with a laptop computer, or perhaps a cell phone. Since laptops and cellphones are so ubiquitous, there would be little additional cost involved for most users. A straightforward approach would be to connect a standard USB-to-microUSB cable between a laptop and the transmitter (the same type of cable and the same jack that would be used to charge its LiPo battery). The laptop (or desktop) would then communicate directly with the transmitter's processor via a USB-to-UART converter. Windows, OS X or Linux should all have standard drivers that would allow them to recognize the serial connection. A simple/standard terminal communication program running on the PC/Mac/Linux machine is all that would be needed to communication with a connected transmitter using a command/response protocol. The following chips are examples of what would need to be added to the transmitter: http://www.digikey.com/products/en?keywords=768-1007-1-ND, or http://www.digikey.com/products/en?keywords=768-1129-2-ND. Those devices are being used in products like this one from Sparkfun: https://www.sparkfun.com/products/13263

A similar interface could be used with a cellphone running Android or iOS. A WiFi TCP-to-UART converter (like this one http://pignology.net/piglet/) could be used to interface the transmitter with any cellphone running an appropriate app. A single wireless converter external to the transmitter could be shared amongst many transmitters.

The external serial/USB interface should also support transmitter firmware updates, and for that reason the same support should be added to the dual-band receiver as well. More fun things to explore.

 

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