Breadboard PSU

breadboard-psuAn initial PSU that I made to insert in a breadboard was a disaster because it was not stable and the jack connection I had with a wall-wart never really made good contact, so i decided to make something better. Initially I was tempted to buy a ready made one at DealExtreme, but as that did not seem to be identical to the one that they pictured, I decided not to. the problem was that the one in the picture did not cover the breadboard, whereas the one that was send out -according to customer reviews-  díd cover the breadboard partly. Add to that that I would have to wait for  the delivery if ordered at DealExtreme, I decided to make one myself, a better one than before and the one at DealExtreme gave me some inspiration.

This circuit is a 5 and 3.3 Volt PSU that can easily be used  for mini breadboards.
It is a more or less standard 5 and 3,3 Volt circuit, but the trick is in the PCB that can be inserted in the PSU rails of the breadboard.

The breadboard I am using has a top and a bottom rail that are isolated from each other. With this circuit and  -and not in the least the PCB- it is possible to give each rail a different  voltage (5 or 3.3V)  or have both rails at 5 Volt.

The circuit is fed from a  wall-wart. Though I have soldered the wires in place, there still is a diode for reverse polarity protection as many wall-warts can be reversed (in polarity) by a switch.

The Vin from the 7805 (and LF33) does not come with a big capacitor but it has a small decoupling capacitor. The 5 Volt has again a decoupling capacitor and a 100uF for smoothing the signal. An LED with current limiting resistor indicates proper functioning. The 3 connectors surrounding the 7805  are forming a 3 pin header  on which the raw Vin, the ground and the 5Volt signal are available.

The 3.3 Volt from the regulator is smoothed with a 100uF capacitor and led to a jumper block that selects between 5 and 3.3 Volt.

Most breadboards have two power rails that each have a positive and a neutral.  In making a PSU that inserts securely in the breadboard it has to use at least 3 spaces. Initially I tried with one, but that just led to enormous frustration.

Because 3 positions deep is a lot to lose on a small breadboard, the PCB need to have some  ‘arms’ to insert in the power rails, leaving the rest of the breadboard free and uncovered.

The Fritzing file of the breadboard is found here. If you don’t have fritzing and don’t want to install it, the print desgin can also be found here. After etching, carefully remove the section of the PCB that falls over the body of the breadboard. Do it such that a minimum of material is removed to keep the arms sticking into the breadboard remain as sturdy as possible.

Then mount the parts and solder those. For the two 2×3 pinheaders that stick in the breadboard, make sure that they match up before soldering them.

The use of the breadboard is not completely full proof: switching between 5 and 3.3 Volt for one rail  is done with a jumper and the only indication that 3.3 Volt is in use is an LED that  is a bit less bright. If you use  both voltages and would still have the rails connected by a wire of some sort, then there will be a short. also, when using both 5 and 3.3 Volt  parts, make sure to not mix up the voltages and blowing up some parts.


Switching low voltage AC with a microcontroller

AC_laagspanningThis circuit can be used to switch a low voltage (12V) AC load with an Arduino or other microcontroller
A positive signal on the entrance will bring T1 into conduction, triggering the Triac via emitter resistor R2. D1 and C1 are just there to provide DC-power to the transistor.
R3 will pull the base low. It can be left out, but it avoids accidental switching when the microcontroller port is undefined (like at start up). I would really advise to put it there.
The Triac should be cooled with a metal profile. remember that the Gate is galvanically connected with the metal housing of the Triac.

WARNING: This is for LOW AC voltage only. Switching a high voltage AC requires use of opto couplers to isolate the High Voltage from the microcontroller.

Notes. I have used an SC141B Triac rather than a TIC206 as I had that around and it is 110 V. max. In a 220 V. country I am not likely going to use that soon for another project.
The picture of the mounted PCB does not show the heatsink yet. It is advisable to use a heatsink.
The printdesign can be downloaded here. There is space for various size capacitors. Mine seems very big but it is a very old one I still had lying around. You may want to move the position of D1 to make it a bit easier to mount a heatsink.
The Diode D1 does not really need to be a 1N4007. The DC part of the circuit does not really need much power. a 1n4148 would be OK, but they have the same price and I had a 1n4007 lying around

Print mounted with components
Print mounted with components

Another Simple Arduino

In its simplest state the Atmega328 can be made to work with a 16 MHz Crystal and 2 small capacitors or even just with a ceramic resonator. Load that with an Arduino bootloader and you have a small arduino compatible microcontroller.
This article describes the building of such a device, on strip board, that can be put together for just a few Euro:

1x Atmega 328 at € 3.40
3x 100nF ceramic capacitors € 0.09
2x 22pF ceramic capacitor € 0.12
1x 16 MHz Crystal € 0.40
1x 100uF 10 V electrolytic capacitor  € 0.12
1x 100uF 25 V electrolytic capacitor € 0.11
1x 1kOhm Resistor € 0.10
1x 10kOhm Resistor € 0.10
1x 330Ohm Resistor € 0.10
1x LED Red € 0.12
1x LED Green € 0.12
pinheaders ca 33 pins € 0.45
1x 7805 € 0.30
stripboard 20x 8
2x 14 pins IC foot € 0.15

The stripboard seen from the TOP/Componentside
The stripboard seen from the TOP/Componentside
The power connections on the componentside of the stripboard
Placing of the 28 IC foot pins on the componentside
Placing of the 28 IC foot pins on the componentside
Placing of  resistors, capacitors, LEDs and jumper. The grey capacitors are 100nF, the brown capacitors are 22pF
Placing of resistors, capacitors, LEDs and jumper. The grey capacitors are 100nF, the brown capacitors are 22pF
Finalised Arduino compatible on stripboard
Finalised Arduino compatible on stripboard

Simple Arduino