number – Page 2 – Experimental Engineering

Posted on May 14, 2014 by The Engineer — Leave a comment

Marine Potable Water Management System

Having two separate water tanks on nb Tanya Louise, with individual pumps, meant that monitoring water levels in tanks & keeping them topped up without emptying & having to reprime pumps every time was a hassle.
To this end I have designed & built this device, to monitor water usage from the individual tanks & automatically switch over when the tank in use nears empty, alerting the user in the process so the empty tanks can be refilled.

Based around an ATMega328, the unit reads a pair of sensors, fitted into the suction line of each pump from the tanks. The calculated flow is displayed on the 20×4 LCD, & logged to EEPROM, in case of power failure.

When the tank in use reaches a preset number of litres flowed, (currently hardcoded, but user input will be implemented soon), the pump is disabled & the other tank pump is enabled. This is also indicated on the display by the arrow to the left of the flow register. Tank switching is alerted by the built in beeper.
It is also possible to manually select a tank to use, & disable automatic operation.
Resetting the individual tank registers is done by a pair of pushbuttons, the total flow register is non-resettable, unless a hard reset is performed to clear the onboard EEPROM.

View of the main PCB is above, with the central Arduino Pro Mini module hosting the backend code. 12-24v power input, sensor input & 5v sensor power output is on the connectors on the left, while the pair of pump outputs is on the bottom right, switched by a pair of IRFZ44N logic-level MOSFETS. Onboard 5v power for the logic is provided by the LM7805 top right.

Code & PCB design is still under development, but I will most likely post the design files & Arduino sketch once some more polishing has been done.

Posted on May 20, 2013 by The Engineer — Leave a comment

Raspberry Pi Geiger Counter

Here’s my latest project with the Pi: interfacing it with the Sparkfun Geiger counter & outputting the resulting data to a character LCD.

The geiger counter is interfaced with it’s USB port, with the random number generator firmware. A Python script reads from the serial port & every minute outputs CPM & µSv/h data to the display.

The Python code is a mash of a few different projects I found online, for different geiger counters & some of my own customisations & code to write the info to the display & convert CPM into µSv/h.

This also writes all the data into a file at /var/log/radlog.txt

The code for this is below:

[snippet id=”1149″]

Posted on December 9, 2012December 9, 2012 by The Engineer — Leave a comment

Safe 4 Tumbler Combination Lock

Just a very quick post with some images of an industrial safe combination lock.

Here the tumblers are lined up to allow the lock to open.

The locking bar has dropped into the slots in the tumbler plates & engaged with the cam.

Rotating the cam pulls the bolt into the lock, allowing the door to open.

The dial screws into the cam plate to allow the mechanism to be operated.

Posted on December 21, 2011December 21, 2011 by The Engineer — 1 Comment

MSR605 3-Track Magnetic Stripe Writer

This unit was bought from eBay to experiment with Magnetic Stripe cards, for little money. This unit is capable of reading & writing all 3 tracks, & both Hi-Co & Lo-Co card types.
Interfaced to a PC through USB, this has a built in PL2303 USB-Serial IC & requires 3A at 9v DC to operate.
The 3 Indicator LEDs on the top of the unit can be toggled by the included software for Power/OK/Fault condition signalling.

Bottom of the unit with the model labels.

Closeup of the model label & serial number.

Here the bottom cover has been removed, showing the main PCB. The pair of large ICs bottom center interface with the magnetic heads. The IC above them has had the markings sanded off.

Closeup of the Prolific PL-2303 USB-Serial converter IC.

Here the connections to the R/W heads are visible, current limiting resistors at the left for the write head, a pair of signal relays, a pair of optoisolators & a LM7805 linear voltage regulator.

Here is the trio of indicator LEDs on a small sub-board.

The PCB has been removed from the main frame here, the only component visible is the rotary encoder.

The rotary encoder has a rubber wheel fitted, which reads the speed of the card as it is being swiped for writing. This allows the control logic to write the data to the stripe at the correct rate for the speed of the card. This allows the unit to write cards from 5-50 inches per second speed.
The Write head is directly behind the rubber pressure roller.

Here you can see the R/W head assembly. The write head is on the right, read on the left. When a card is written to, it immediately gets read by the second head for verification.

The drivers for this unit are also available here: Magcard Writer Drivers

Posted on March 8, 2011February 11, 2011 by The Engineer — Leave a comment

USB Multi Card Reader

Here is a cheap USB 8-in-1 card reader. Power & Access LEDs are on top left.

Top of the PCB. The OTi IC is the interface IC to the USB port, part number is OTI002126. Card sockets on the top here are CF/Microdrive & Memory Stick.

Bottom of the PCB with the SD/MMC, Smart Media

Posted on December 6, 2010 by The Engineer — Leave a comment

Southwestern Bell Freedom Phone

This is an old cordless landline phone, with dead handset batteries.

Here’s the handset with the back removed. Shown is the radio TX/RX board, underneath is the keyboard PCB with the speaker & mic. All the FM radio tuning coils are visible & a LT450GW electromechanical filter.

Radio PCB removed from the housing showing the main CPU controlling the unit, a Motorola MC13109FB.

The keypad PCB, with also holds the microphone & speaker.

Bottom of the keypad board, which holds a LSC526534DW 8-Bit µC & a AT93C46R serial EEPROM for phone number storage.

Here’s the base unit with it’s top cover removed. Black square object on far right of image is the microphone for intercom use, power supply section is top left, phone interface bottom left, FM radio is centre. Battery snap for power backup is bottom right.

PSU section of the board on the left here, 9v AC input socket at the bottom, with bridge rectifier diodes & main filter capacitor above. Two green transformers on the right are for audio impedance matching. Another LT450GW filter is visible at the top, part of the base unit FM transceiver.

Another 8-bit µC, this time a LSC526535P, paired with another AT93C46 EEPROM. Blue blob is 3.58MHz crystal resonator for the MCU clock. The SEC IC is a KS58015 4-bit binary to DTMF dialer IC. This is controlled by the µC.

Underside of the base unit Main PCB, showing the matching MC13109FB IC for the radio functions.

Posted on August 25, 2010 by The Engineer — Leave a comment

Ericsson GA628

Here is a phone from the mid 90s, the Ericsson GA628. Here visible is the front of the unit with keypad, & single line monochrome LCD for number display.

Here the battery is removed from the phone, showing the SIM card socket. At the top under the antenna stub is the socket for an external antenna.

Here the front is removed from the phone, PCB on left, rear of keypad on right. Microphone is at bottom of keypad, with speaker at the top. Top right of the PCB is the ringer buzzer, left is shield for RF amplifier.

Here is the back of the main PCB, RF sections on left & centre. Processing & memory on right.

This phone had a Ni-Mh battery, before Li-Ion batteries were introduced.

The LCD from the front of the phone is shown here. A simple dot matrix single line unit.