Quick Power Supply 'update'
<This project requires further documentation>Hardware:
|parallel lcd||Simple Cheap lcd Character Display. HD44780 Compliant. Found in unknown state|
|atmega 48||Super Cheap DIP Microcontroler. Programmed with AVR ISP MK2. Tacked to a protoboard.|
|Misc Components||Resistors, Caps, led, potentiometer (10K)|
|Routing the outputs||For
some reason the outputs of the
supply were in the rear, some low gague wire and scavenged banana jacks
later, they were re-located to the front.
The supply was also mounted onto aluminum risers to allow proper ventilation, the probably source of the failure of the previous supply
|Finding Some Power||To
drive the lcd,
microcontroller i will need 5v. After some trace-following and careful
observing, a low voltage winding from the main transformer was
rectified and dumped into a 2200uf cap. nominally, the cap stayed at
10V DC. Upon probing the cap, i found that there was little AC ripple.
Next i made some assumptions and tested them. i banked on having the
lcd and micro would consume 100ma at 5V. to simulate this (from the 10V
cap) i used a xxx ohm resistor. THIS
IS IMPORTANT. I checked that the power supply preformed well
with this extra internal load. There was no observable difference in
the power supplies output, even under load. I now had 10V, one 7805
away from a stable 5V supply.
It is also important that the ground of the cap is the same as the ground of the supply output
|Testing the LCD||As
this LCD was
found in an unknown state, it was a good idea to test to see that it
worked before designing everything around it.
Emily K was nearby, thus the lcd statement. LCD is driven in 4 bit mode (instead of 8 bit mode). Contrast was set by small blue potentiometer (as seen behind lcd screen)
|Operating at Higher Voltages||The A/D on the AVR is 5 V tolerant, not 55V, a simple resistive divider from the output of the supply was used. Note at this point the lcd was temporairally mounted into aluminum rectangle-bar.|
|Calibration||A multi-meter (outside of image) was used to calibrate the multiplier used to convert ADC counts to Voltage outputs|
Schematic / Setup:
|Linear reg supply||...|