Skip to main content

Slave Flash for Underwater Camera


The flash module in this circuit comes from a  Fuji disposable camera. The author’s design  is based on various ideas on this subject that  can be found on the Web. The guide number  [1] of the flash is approximately 14 in the air  and close to 6 underwater. The flash intensity  is not adjustable.

Slave Flash for Underwater Cameraqq

This flash unit is primarily intended to be used  for underwater photography, which is why  the author fitted it in a  case originally used for  a Nikon Coolpix 7900.  Of course, it can also  be used for dry-land  photography. The flash  module is powered by  a 1.5-V battery, which  must supply approximately 30 to 40 mA  to charge the capacitor. The control portion is built around a  PIC12F675, which is  powered by a 3-V button cell. Its current consumption is practically negligible  just a few  milli amperes while the flash is active and only  600 nA the rest of the time, when the micro-controller is in the standby state. For this rea-son, the unit does not have an on/off button. The flash from the Fuji camera is triggered by  a mechanical contact that is actuated at the  same time as the camera shutter. Here this  contact is replaced by an MCR-100-8 thyristor with a 1-kΩ resistor in series with the gate.  These two components are fitted directly on  the Fuji flash module.

Slave Flash for Underwater Camera Circuit Diagram

There are many different types of disposable  camera, each with its own type of flash module. However, these modules are all similar,  so you can easily adapt the design described  here to whatever type you can put your hands  on. Pay attention to the voltages, and don’t forget to connect the grounds of the flash  PCB and the logic circuitry together. Schematics for many of these flash modules are  often available on the Web, so it shouldn’t be  difficult to find something close to what you  actually have.

The firmware [2] has three operating modes:  manual, pseudo-TTL (through the lens,  which means that the light level is measured  through the lens) and sleep. In manual mode the flash it triggered when you press the shutter button. In pseudo-TTL mode there are a  few short flashes before the main flash (commonly used for red-eye reduction). The number of pre-flashes varies from one camera  to the next, and even from one shot to the  next. In pseudo-TTL mode, the firmware gets  around this problem by waiting for 100 ms  after the first flash before it tries to detect  the exposure flash. LED D1 lights up if the pre-flash has been detected  but the main flash has  not been detected after  the 100-ms delay.

The contribution of the  slave flash to the expo-sure of the subject is not  included in the measurement made by the  camera, but instead  simply adds to the light  from the master flash –  hence the designation  ‘pseudo-TTL’. Although  the author considered  the option of a true  TTL design, or at least  adjustable flash intensity, this requires a very  specific transistor (25AAJ8 or equivalent) that  is very difficult to obtain.

Author : Daniel Savel  – copyright : Elektor


Labels:

Comments

Post a Comment

Popular posts from this blog

OP AMP INTEGRATOR CALCULATOR

Enter the Input Voltage,Vin: Volts Enter the Frequency, f: Hertz Enter the Input Resistance, Rin: Ohms Enter the Value of Capacitor, C: Farads Output Voltage, Vout: Volts OP AMP based Integrator Tutorial and Design
Post a Comment
Read more

Block diagram of AM transmitter and receiver with explanation

Block diagram of AM transmitter and receiver with explanation AM Transmitter : Transmitters that transmit AM signals are known as AM transmitters. These transmitters are used in medium wave (MW) and short wave (SW) frequency bands for AM broadcast. The MW band has frequencies between 550 KHz and 1650 KHz, and the SW band has frequencies ranging from 3 MHz to 30 MHz. The two types of AM transmitters that are used based on their transmitting powers are: ·          High Level ·          Low Level High level transmitters use high level modulation, and low level transmitters use low level modulation. The choice between the two modulation schemes depends on the transmitting power of the AM transmitter. In broadcast transmitters, where the transmitting power may be of the order of kilowatts, high level modulation is employed. In low power transmitters, where only a few watts of transmitting power are required , low...
Post a Comment
Read more

Using the TLP250 Isolated MOSFET Driver Explanation and Example Circuits

I’ve already shown how to drive an N-channel MOSFET (or even an IGBT) in both high-side and low-side configurations in a multitude of ways. I’ve also explained the principles of driving the MOSFETs in these configurations. The dedicated drivers I’ve shown so far are the TC427 and IR2110. Some people have requested me to write up on MOSFET drive using the very popular TLP250. And I’ll explain that here. The TLP250, like any driver, has an input stage, an output stage and a power supply connection. What’s special about the TLP250 is that the TLP250 is an optically isolated driver, meaning that the input and output are “optically isolated”. The isolation is optical – the input stage is an LED and the receiving output stage is light sensitive (think “photodetector”). Before delving any further, let’s look at the pin configuration and the truth table. Fig. 1 - TLP250 Pin Configuration Fig. 2 - TLP250 Truth Table Fig. 1 clearly shows the input LED side and the receiving photodetector as well...
Post a Comment
Read more