Flow PDA

Custom Open Source PDA with Android support and additional hardware for Research.

In this article we shall be describing all of the hardware features of the FLOW G1.5 in detail as well as mentioning general information about the Gizmo it self. After reading this article you should have a better understanding of the features available on the device ether you are a hardware specialist or not.

We shall be describing here all available features of the Flow G1.5 Gizmo as well as differences from the original G1 device. There are many new features as well as allot of rework on the enclosure and the PCB design. Some features have been removed and others added for decreasing the end price as well as for practicality reasons.


External Differences

As you can see from the above images the 1.5 generation Flow has many external differences from it's predecessor G1. These Differences are described as follows:

1.  External dimensions are: 116mm x 68mm x 18mm

2.  2 Top buttons have been removed for practicality reasons due to unnecessary functionality

3.  Status indication LED's have been added to the Top left side of the enclosure to indicate GSM & charging features

4.  Headphone Jack has been moved to the Top side of the device for ease of use.

5.  Speaker position changed and Speaker holes for best sound have been added

6.  640x480px camera has been removed leaving only the 1.3mp camera on the back

7.  Flash has been removed due to unnecessary functionality

8.  Enclosure has been redesigned for better structure as well as easier access and Assembly/Dis-assembly

9.  Decals have been added to the enclosure for easier understanding of each slot as well as Gizmo For You logo added on the back side of the enclosure

10.  2 Colors used for the enclosure - Black Matte and Silver, no Clear coating required

Hardware Differences

Not only the external look of the device has changed, everything has been redesigned from scratch and repositioned inside the Gizmo. Some components removed and others added. Below is the full list of available hardware features of the device:

1.  LCD - 480 x 640 px with Resistive Touchscreen (Unchanged), LED Driver changed for less components and better availability. LCD support added for best alignment with the enclosure. 

2. ZigBit 900MHz RF Module has been added to expand the applications for the device.

3.  Sound - Mono Speaker out & Stereo Headphone out with Auto off when headset is plugged in

4.  Battery Capacity - 1500mA Li-Po Battery in an Ultra Slim profile of 3.2mm

5.  Battery Charging - 400mA Charge rate through Power Supply of the device (USB Charging removed due to high capacity required to be charged)

6.  Camera - 1.3mp, no expansion PCB's required since the FLEX connector plugs directly to the FLOW G1.5 PCB.

7.  Power Management reconstructed with less components & optimized design.

8.  Single PCB design - reducing the cost and practicality in assembly

9.  GSM & GPS antennas as well as GSM module & Sim Card moved to the bottom of the device for better reception and reduced noise.

10.  Sim Card slot changed to a PopOut Slot with thinner profile.

11.  24pin connector reduced in IO count leaving only the necessary signals for development (Power, USB & Development cables from G1 unit are fully compatible with only difference in IO names of the Development cable)

12.  Internal Stability of the PCB increased with Mounting holes and holding brackets.

13.  6 Layer PCB design with optimized track placement & better shielding for noise reduction and sound improvement.

14.  General purpose buttons changed for softer and more accurate pressure assignment.

15.  BGA components removed for easier soldering, debugging and lower price.

16.  HDMI Out has been added through the 24pin Connector.

These are the differences of the G1.5 unit from G1. All features and designs have been made as described above for a more affordable end price as well as practicality issues and more reliable operation. We hope that these changes are only for the best of the FLOW project and that everyone benefits from the changes and improvements we made.

So let's recap. We have said what is changed and what isn't but not everyone is familiar with the previous versions and it is best to summarize all the features. So here they are, features and specifications for the FLOW G1.5:

1.   480 x 640 pixels 3.7" LCD with a resistive Touch- Screen

2.   HDMI Out through the 24pin connector

3.   1.3mp Camera

4.   ZigBit 900MHz RF Transceiver with internal antenna

5.   UC864-G Module (GSM-GPS-GPRS-UMTS with all antennas included)

6.   Mono Speaker for Audio

7.   Stereo Headphone Jack 3.5mm

8.   Triple Axis Accelerometer

9.   Battery Monitoring & Status (Temperature, Capacity and other info)

10.   1500mA Li-Po Battery in an Ultra Slim Profile of 3.2mm

11.   400mA Fast Charger (only though power supply)

12.   Vibrator Motor

13.   Device can be selected with the UC864-G module or without

14.   Device can be used with the Overo Fire or Overo Earth (it can be used with any one of       the Overo platforms but we only supply the Fire and Earth options in the shop)

14.1 Overo Earth Specifications are:

OMAP 3503 Application Processor with ARM Cortex-A8 CPU
600 MHz
Up to 1200 Dhrystone MIPS
256MB Flash
- on-board microSD card slot
- I2C, PWM lines (6), A/D (6), 1-wire, UART, SPI, Camera in, Extra MMC lines.
- Headset, Microphone, backup battery, - USB OTG signals, USB HS Host
  (Please consult the Forum or check out the schematics to see how these signals are connected to FLOW G1.5)

14.2 Overo Fire Specifications are:

OMAP 3530 Applications Processor with ARM Cortex-A8 CPU, a C64x+ digital signal processor (DSP) core, and the POWERVR SGX for 2D and 3D graphics acceleration
600 MHz
Up to 1200 Dhrystone MIPS
256MB Flash
- on-board microSD card slot
- I2C, PWM lines (6), A/D (6), 1-wire, UART, SPI, Camera in, Extra MMC lines.
- Headset, Microphone, backup battery, - USB OTG signals, USB HS Host
(Please consult the Forum or check out the schematics to see how these signals are connected to FLOW G1.5)
Wireless Communication:
802.11(g) and Bluetooth®

15.   2 x General Purpose buttons (By default assigned to Home & Back in Android)

16.   Android Eclair Operating environment (at the time of his writing)

17.   External dimensions are: 116mm x 68mm x 18mm

18.   Simple and rigid enclosure with internal PCB support as well as support for all internal components. Enclosure is Colorized as seen on the picture above. (Custom colorization for larger quantities is available)

19.   6 Layer 1.2mm thick PCB Design with carefully routed tracks and shielded with Power planes.

20. Customizable internal switches for envelopment and debugging.

External Features

As you can see from the below image there are several slots and connections that are located on the exterior of the device. These features are important to know as well as the direction of the insertions that they have.

3.5mm Headphone Jack

The headphone jack uses the Right and Left signals of the audio output and can be used for listening audio on the device. Once the headphone set is connected, the on board speaker is disabled along with other audio hardware so that only the headphone signals are used. The connector it self has few millimeters of extrusion from the case so that any 3.5mm headphone jack can be used without interfering with the enclosure it self.

Status LED's

There are 3 LED's on the Top Left corner of the device as shown on the picture above. These LED's are used for displaying the status of various functions of the device.

Charger In - This LED indicates if a charger has been plugged into the device and that it is getting the necessary power for charging the on board battery. Although a simple function, it helps quickly realize if the charger is plugged in or if the device is functioning as it should.

Charge Stat - Indicates if the battery is still charging or if the charging cycle is finished. When this LED is ON then the battery is being charged and when the LED is OFF then the battery is no longer charging or doesn't need additional charge.

GSM Stat - This LED indicates the different states in which the GSM module is functioning. Fast flashing indicates that the module is searching for GSM networks. Slow Flashing indicates that the network is found and the device is ready to make phone calls. This will also be indicated in Android it self with the cellular signal bars on the top status bar on the screen. You can find additional information about GSM LED states in the Documentation of each GSM module from Telit.

microSD Card

The microSD slot is located as shown on the image above. It should also be inserted as shown on the picture. Please note the direction and orientation of the card when inserting it. The card can be inserted as easy as it can be removed thanks to the pop-out slot on the Gumstix platform it self.

Sim Card

There is no limitation on the carrier that can be used with the GSM module and any Sim card can be inserted. Please note the orientation of the card from the above image. Inserting this card is as easy as the microSD. The Sim slot on the device has a pop-out spring mechanism and can be bushed in for inserting or removing it. The Sim Slot it self is categorized as an 8 position slot, meaning that all 8 pins of the card are connected to the slot it self. However only 6 pins of the card are used as commonly designed on most cellular devices.

24pin Connector

We use the 24pin connector in all our current FLOW devices. This connector has many signals that can be used for many applications and shall be described later on in this article. In this part of the description just have in mind that that is where the connector is located.


There are 3 buttons on the FLOW G1.5 and have the functionality as described below.

Power Button

The Power button does pretty much what it is named after, it powers the device ON and OFF. When powering the device ON just hold the button for 1 - 2 seconds and release, FLOW should power ON and begin loading the Operating System.

If you wish to place the device in a Locked Mode (sleep mode) to consume less power (which is also done automatically after some idle operational time) then simply press and release the button for 1 second.

To completely Power OFF the device simply press and hold the power button until the device is turned OFF. This period may vary on different revisions of the UI firmware but generally this takes from 4 - 6 seconds.

Back & Menu Buttons

These 2 buttons are used to navigate through Android it self and are mapped to the names they are named after. In different applications these buttons may have different functionality.

Hardware Features

Now that we covered the external features of the device we shall describe every significant component as well as it's functionality in overall and different options available to change it's functionality.


We used the same LCD as on the previous version of the FLOW (FLOW G1) due to it's good resolution and size as well as the on-board Touch-Screen.

The LCD has the following features:

Resolution - 480x640 px (Portrait) - 16bit

Size - 3.7" Diagonal (Viewing Area of 74.88 x 56.16mm)

Touch-Screen - Resistive


As an additional feature, we have included an HDMI - out on the FLOW G1.5 and the device can be connected to an external display for viewing images, videos or other media the same way as it would be displayed on the LCD. Please have in mind that this feature only outputs Video and no Video IN is available on the device. Also have in mind that since there is an accelerometer on the device for display orientation, it is best to rotate the device in landscape mode for better image on an external display.


By Default on FLOW G1.5 there is an RF Transceiver which has the following key features:

o - High RX sensitivity (-110 dBm)

o - Outperforming link budget (120 dB)

o - Up to 10 dB output power

o - Low power consumption

o - IEEE 802.15.4 compliant

o - 868 / 915 MHz band

o - BitCloud embedded software, including UART bootloader and AT command set

The Transceiver uses an internal Chip Antenna which has a small profile and is ideally suited for this application.

The Transceiver it self can be controlled through the Serial as well as SPI interfaces through internal switches on the PCB. Have in mind that by default these switches as disconnected if a GSM module is selected. If no GSM module is selected then the Serial Switch is used to control the RF Transceiver.


We have a selection of GSM modules that can be used with FLOW G1.5


This module provides the ability to use GSM as well as GPS features on the FLOW. Main features of this module are:

o - HSDPA 7.2 Mbps (Controlled though the USB HOST interface of the Overo series of platforms)

o - UMTS/HSDPA (WCDMA/FDD) 850/1900/2100 MHz

o - Quad-Band EGSM 850/900/1800/1900

o - GPRS multi-slot class 12

o - EDGE multi-slot class 12

o - GPS High Sensitivity for indoor reception of up to -157 dBm

o - GPS Accuracy < 3m

o - GPS Supports 12-Channel GPS, L1 1575.42 MHz

o - GPS Low Power consumption


If this module is used the the features are the same as described above with the difference of not having the GPS

GSM Antenna

The antenna used on the FLOW G1.5 is an SMD antenna, operates on 880~960 MHz, 1710~2170 MHz has impedance of 50 Ohm and linear polarization. Antenna has the appearance as shown below.

GPS Antenna

The Active GPS antenna has the size of 10 x 10mm, has 25dB LNA gain. It connects to the UC864-G through a U.FL connector and has a separate place inside the enclosure.

The antenna has the appearance as shown above.

Please have in mind that all required antennas are included with each option you select when purchasing the FLOW G1.5 according to needs for each situation.


By default there is an internal camera on the FLOW G1.5 which has a resolution of 1300 x 1040 pix (1.3 Mp). It operates with 15 fps ans is directly connected to the 27pin connector on the Overo platforms. The new revisions of the Overo platforms have the 27pin camera connector in the same place, meaning that any Overo platform can be used for connecting the camera on the FLOW G1.5 motherboard although we only offer the Overo Fire and Overo Earth options in our shop.


FLOW G1.5 has an internal speaker for listening to Audio on the device. This Audio is Mono, unlike the Headphone connections which are Stereo. The reason we used only one of the signals for an external speaker is that the profile of the device is small in size and there was no need to have 2 speakers and unnecessary components since the Stereo effect would be unnoticeable.

Naturally there is also a separate speaker for the GSM functionality as well as a microphone for cellular conversations.


There is a 3 - Axis Accelerometer on the FLOW G1.5 with Tilt functionality. The accelerometer is ideal for controlling the orientation of the screen as well as used in other applications of the Android platform. The analog signals of the accelerometer are directly connected to the Overo platform. A more detailed information on what accelerometer is used and how it is connected you can find in the schematics of this project in the Files section.


Power for the entire device is controlled through our UI interface which is a PIC16LF88 Micro-Controller. All voltage regulators and switches are connected to this IC. The Micro-Controller communicates with the Overo platforms through the I2C interface and indicates the status as well as controls the power consumption of the device.


The battery used on the Gizmo is a 1500 mA Li-Po battery with a very thin profile of 3.2mm. The battery can be charged with the on-board charger at a rate of 400mA. Another important feature to notice is that there is a separate IC which monitors the battery status (discharge rate, voltage, temperature) and indicates all this information in Android through the 1Wire interface available on the Overo line of platforms.

24pin Connector

On all of our FLOW Gizmos we use a 24pin connector to output important signals for debugging, development and general use. From FLOW G1 some signals have changed, although Charger, USB and Development cables are all compatible with any FLOW platform.

The signals of the connector are as shown on the image above. If you are familiar with the previous signals on FLOW G1 you shall notice that some signals are removed and only the necessary ones are left. Also since we now support the HDMI feature, these signals are now occupying the connector as well.

Overo Platforms

The Gumstix Overo line of platforms of what drives the FLOW G1.5 It is a complete processing module with a Processor, RAM, FLASH and other features. Although there are 4 available Overo platforms (at the time of this writing) from Gumstix, we are providing only the 2. We believe that these 2 platforms are ideally selected for a low budget and Low Specification device as well as a Full specification one. Below is the list of the Key features for each of the Overo platforms we have available as options for the FLOW G1.5

Overo Earth

Processor - OMAP 3503 with ARM Cortex-A8 CPU

Clock - 600 MHz

Performance - Up to 1200 Dhrystone MIPS

RAM - 256 MB

FLASH - 256 MB

Overo Fire

Processor - OMAP 3530 with ARM Cortex-A8 CPU, a C64x+ digital signal processor (DSP) core, POWERVR SGX for 2D and 3D graphics acceleration

Clock - 600 MHz

Performance - Up to 1200 Dhrystone MIPS

RAM - 256 MB

FLASH - 256 MB