Monday, March 21, 2016

Low voltage power supply unit

In this post we introduce simple and flexible, regulated low voltage power supply unit. This power supply has provision for 4 outputs such as 1.5V, 1.8V, 2.5V and 3.3V. We mainly build this low voltage power supply unit to test (and power-up) low voltage MCUs, CPLDs and radio receivers. For this power supply we choose 1.8V, 2.5V and 3.3V to get it compatible with most of the LVTTL/LVCMOS devices. Other than that, we include 1.5V because there are several analog ICs are available for that voltage level.

This power supply unit is based on LM1117/AMS1117 voltage regulator series and for this design we use AMS1117-1.5, AMS111-1.8, AMS1117-2.5 and AMS1117-3.3 fixed voltage regulators. Except to above regulators this board can be use with AMS1117-2.85 and AMS1117-5.0 regulators.

Internal view of low voltage power supply unit.

In our prototype we use center-tapped 6V (1A) step down transformer with this power supply unit. All the wiring diagrams to transformer and rotary switch are provided with the schematic.

The given PCB design for this power supply unit is based on SOT-223 (SMD) version of voltage regulators. Even though it use SMD components this PCB can build with single side PCB. Dimension of the PCB is set to 89mm × 69mm. All PCB designs and schematics of this power supply unit are available to download at elect.wikispaces.com.

Friday, March 11, 2016

Mullard 3-3 Amplifier Project (Part 3)

This is quick (and final) post regarding our Mullard 3-3 audio amplifier project.

In last few months we got several e-mails regarding this project and most of the people are asking for modified schematic related to this project. The schematic of our amplifier is available to download in here. Please note that this schematic is heavily based on original Mullard 3-3 amplifier design and main component which we replace in that original schematic is it's tube base power supply unit.

As a final step of this project we construct wooden enclosure for that amplifier and attached it to 10 inch (8Ω) full range speaker. High resolution photographs of our amplifier is available in here.

Final view of Mullard 3-3 audio power amplifier

As a conclusion this Mullard 3-3 audio power amplifier is high quality low power tube amplifier with minimum complexity. We really impressed with it's audio quality and overall performance.

Tuesday, March 1, 2016

Artificial star unit

Star test is the most recommended method to test and collimate telescopes. To do a "star test" we need to aim and track telescope with real star and most of the times this is quite difficult to do because of fast movement of stars and bad sky conditions. Another problem with real star is air turbulence and some times this effect may leads to false conclusions.

However artificial star is an excellent alternative for "real star test" and in this post we introduce easy to build "artificial star unit" to test and collimate telescopes. This unit is based on commonly available electronic components and it can operate with 9V battery. At the time of writing this unit can build around LKR 1000.00 (Approximately 7.00 - 8.00 USD).

In this given design we use NE555 timer IC to generate PWM output to LED and this allow us to control intensity of the artificial star. In our prototype we use high-bright 3mm white LED as our light source.

Apart from circuit the next most important thing in this unit is it's LED mounting. Since real star appears like "point of light" this artificial star must appear as a point of light. To archive this same effect we dill 300 micron (0.3mm) pin-hole in our casing as shown in below.

Prototype version of artificial star unit. Output pin-hole is located in left side of this box.

We test and collimate several telescopes with this unit, which including 8'' and 10'' Newtonians, 6'' and 11'' Schmidt-Cassegrain telescopes. Now we use this unit periodically to test our scopes for collimation and related issues.

PCB, schematic and wiring diagrams of this "Artificial Star Unit" is available to download at elect.wikispaces.com.