In a previous article we introduced the first uCHobby designed kit. The SBBPWR1 is a handy power supply module which plugs directly into a solderless breadboard. The previous article detailed the the overall design process for this kit. The SBBPWR1 has been received well and we got several good suggestions for improvements.
This article describes the improvements for the second revision of the kit. The new version is called SBBPWR2.
Picture above is the new SBBPWR2 board with the SBBPWR1 shown below. The pictures are not at to scale but you can tell that the SBBPWR2 is wider and includes some header pins along the center area. Both boards have the outer header pins that pick up power rails on the breadboard. On the older board the VIN and VADJ signals were brought out to two inner headers. The new board replaces these two inner headers with four (4) headers that plug in like an IC would. This change adds stability to the board and provides an option for use on breadboards that don’t have the correct spacing on the power rails.
Larger Board Size:
The board is wider to accommodate more header pins in the center area.
Voltage Selection Jumper:
Several comments compared the SBBPWR1 board to some other similar kits which has a switch to change the voltage. We considered changing the power switch to one of these three position switches so you could select between off – 3.3 and 5V but opted to put a jumper on the board instead. The LM317 VADJ voltage divider is made up of 3 resistors on the SBBPWR2, one of which can be shorted with a removable jumper. We supply the resistors to make this select between 3.3 and 5V with 3.3 as the jumper off selection.
The idea here is that you would not damage your 3.3V parts when you meant to turn off the power supply. The voltage selection on the power switch just did not seem safe to us. With the Jumper you can decide which voltage you need in your project and then use the simple on/off power switch safely.
You can change the voltages and use the jumper for selection as well. Maybe you want 9V/5V or 12V/6V. You just need to install the correct resistors to make this happen.
Inner Header connections:
The original board was a bit unstable, it wobbled on the connection headers so we placed some header connections along the center. This change makes the board stay put very well.
Support for other power rail spacing:
There is some variability in the spacing of of the power rails on breadboards. Most of the ones I have seen work fine with spacing we chose, but some of the less-expensive models such as those from Radio Shack have a slightly different spacing. The SBBPWR1 was not convenient for those boards, as you could use a single header set to connect to power rails on one side only. To address this issue a set of header connections were included along the center for the SBBPWR2. You could leave off the outer power headers and use the inside set on these boards. You have to place your power rail jumpers then plug in the SBBPWR2.
Moved the VIN and VADJ signals:
The original inner two connection headers for VIN and VADJ were moved to the center area so they could plug in much like an IC would. Moving these connections make the board more stable. The VIN signal provides access to the filtered and polarity-adjusted input voltage. This is ideal for applications where you don’t need regulated voltage for something like a motor. The VADJ signal is the adjust pin on the LM317 regulator. You can use this signal to make a current source or to supply an external voltage adjustment.
Fixed Lead Spacing Problems:
The lead spacing for the DC power jack and the large filter cap (C1) were tight on the SBBPWR1.
Higher Voltage on C1:
The input filter cap has changed. The SBBPWR1 used a 25V cap that was not easy to find. The SBBPWR2 uses a more common 50V cap which is better suited to this application. The LM317 can take a maximum of 40V on its input so the 25V cap was limiting the options. Now you should be able to use higher voltage wall warts.
Larger Pads on many parts:
Several of the pad sizes were increased for SBBPWR2. Where ever possible the pad size was increased and where spacing was tight we made the pads oval. This makes the board much easier to solder. We want this to be a good first kit and some of the lead spacing created a soldering challenge. The SBBPWR2 is very easy build now.
We had this idea that some larger holes next to the inner header pins would make it easier for someone to line up the SBBPWR2 with power jumpers used under the board. This does work but you need a bright light under the board edge to see well. But there was a great unexpected benefit with these holes. Jumper wires pass though the holes and plug into the breadboard just fine. If you do not mind seeing the jumpers, you can easily pickup the inner signals just by plugging your jumper wire though the hole. It really does work well.