FlashTime
FlashTime is a light flash generator synchronized with the PPS (Pulse Per second) of a GPS. It allows to generate light pulses to be recorded in the recording of an astronomical event with an accuracy of a few microseconds. Its use is very simple and the display and keyboard help to navigate and configure the events and operating parameters.
Internally it uses an Arduino Uno and a GPS board with Shield for Arduino. The box is the result of 3D printing. Its entire design is intended to be easily fabricated by oneself.
Construction of the equipment:
The elements necessary for its construction are:
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Arduino UNO
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LCD 1602 keypad Shield : there are different manufacturers that offer seemingly compatible options but differ slightly in mechanical and electronic aspects.
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Adafruit Ultimate GPS Logger Shield: GPS board with PPS (Pulse Per Second) and integrated antenna
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9V battery and clip
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Switch
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Red LED and resistor
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DC 5.5mm male and female connectors
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Bipolar cable
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Box
The electronics are very simple. The board containing the display and the keyboard is placed in “sandwich” mode using the rows of pins included in the Arduino UNO. The connection to the Adafruit Ultimate GPS Logger Shield must be wired according to the schematic shown below:
For the assembly of the set, some constructive aspects must be taken into account, such as those indicated below:
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As already mentioned, the Keypad Shield is connected to the Arduino in sandwich mode, but the GPS Shield will be placed in the box separately so that the antenna is facing up and separated from obstacles that prevent signal reception.
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The 9V battery clip is soldered to the pins of the power connector, sandwiching in one of the wires a switch.
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The switch will be placed on a wall of the box by drilling the corresponding hole.
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The led with its series resistor is connected to a sufficiently long cable (the led will have to be placed in the mouth of the telescope) and the end is soldered to a 5.5mm DC connector.
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The pin 3 of the Arduino (output for the flash) is connected together with GND to a female DC connector that will be placed on a wall of the box by drilling the corresponding hole.
The different elements of FlashTime can be integrated into a box as desired. In my case, I have opted for the following solution:
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For the box, this design accessible on the Internet has been selected: https://www.thingiverse.com/thing:1734148
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The .stl files do not include the top cover, which has been designed separately.
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When printing the main body, I did not remove the back and side openings.
Use of the equipment:
The startup screen shows the program version. At startup, a 2-second flash of the LED is generated to check that the program is working correctly. This flash is NOT synchronized, it only serves to verify the operation of the LED.
Staritng:
Keyboard:
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CONFIG: enters configuration mode. Each time it is pressed, a new parameter is displayed.
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SAVE: saves the configuration.
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RESET: initializes the program. It is a mandatory option after having configured and saved parameters.
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UP and DOWN if the CONFIG key has been pressed allow to increase or decrease the parameter to be configured. Outside the configuration mode it allows to access the GPS data screen and return.
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FLASH: generates a synchronized flash as explained below.
Screens after starting:
Displays the scheduled event, indicating date and UTC time.
Displays the values set for:
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Cap: (capture) how long before the event the capture should start (and symmetrically after the event).
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Int: (Interval) how long before and after the event a flash is to be generated
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Flash: duration of the flash
Displays the current UTC time:
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GPS indicates that a signal is being received. If instead of GPS --- is displayed, there is no GPS signal yet.
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“event finished” indicates that the event has elapsed, otherwise it will show a countdown (see next page).
Waiting an event...
If the event has not yet elapsed, it will display a countdown in seconds with one of these status:
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To start: seconds remaining until capture should start
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To flash: seconds left until first flash
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To event: seconds remaining until the event
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To flash2: seconds remaining until the second flash
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To end: seconds left to finish recording
Parameter configuration:
With the CONFIG key we can move from parameter to parameter to be configured. For each parameter, the UP and DOWN keys are used to modify the value.
Display of latitude, longitude and altitude data
Displays latitude/longitude (first line) and altitude (second line). Values are updated in real time, once per second.
Flashes generation (without configuring event)
Pressing the Flash button causes a 3s flash coinciding with the 30th or 00th second (whichever comes first).
This option allows to generate a flash synchronized with the PPS without the need to program an event.
Remarks
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The unit can be powered from the USB port of the PC or by a 9V battery (internal) activated by a switch.
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In order for the unit to acquire GPS satellite signals, nothing should be placed on the top cover that may hinder signal reception.
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The intensity of the display backlight is adjustable with a parameter in the configuration mode. Once modified, as for the rest of the parameters, it must be reset (RESET key) to take effect.
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To update the firmware via USB from a PC, it is necessary to first remove the top cover and change the position of the micro-switch on the GPS board. At the end of the firmware update it must be returned to its normal position.
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The LED to generate the flashes is connected on one side. It is advisable to make sure that the LED lights up for 2 seconds when the unit is started, to make sure it is working properly.
