# How do I power a device with a 4-directional 4-pin connector? I have an idea and I would like you to point out what's wrong with it

Let's say I have a matrix of square 12.7 mm cells. Every cell is a connector to which an independent little piece ("little piece" is a building block) may be connected. Actually, it's a little puzzle/sandbox game (a hobby project) where you have to build a circuit out of small building blocks like wires, logic gates, sensors and so on.

Every little piece has 4 contacts connected to it: +5V, CLK, RST, GND. Originally I wanted to make 4 rings: the inner is RST, then CLK, then +5V, then GND.

I'm planning to make the little pieces as PCBs at some cheap prototyping website or just at home. Making a PCB for the connector board is an overkill and will be quite expensive. I could buy some perfboard on Aliexpress and solder everything but this would be too prototypish, IMO. On the other hand, connecting the 4 rings or similarly put pin sockets in some plastic container with holes is very complicated, so I decided to switch things up a bit.

Now I have just 4 pins. Pins A, D are both =RST, and pins B and C always have different values: CLK and ~CLK. Therefore, the little pieces can go either way, and that's important. The little things would identify which two pins are complementary CLKs and which are RST using an XOR gate. The power is collected into a capacitor through a bridge rectifier in case both CLK and ~CLK go low or if the piece needs extra current.

simulate this circuit – Schematic created using CircuitLab

This is the internals of a "little piece":

simulate this circuit

My questions are:

1) Are there easier ways to do this? Are there readily available sockets or designs for my purpose?

2) What obstacles and problems will I encounter actually designing everything (apart from size constraints, although I can make a little piece occupy several cells)?

3) How to choose the right R and C values for a given frequency?

• You're referring to different components/things with the same word "pieces". Please be more specific for us to be able to understand what you're trying to achieve. If these "square 12.7mm pieces" are something that readily exist, providing a photo that shows what you're referring to would help. If the "little puzzle/sandbox game" you're referring to also exists and has a name please edit your post to contain that information ! – Juan Manuel López Manzano Aug 3 '18 at 18:02
• Draw one schematic, the schematics above might make sense to you but is unclear what you are trying to design. There is schematic tool available (button above question dialog when asking questions). Also be more specific in your questions, "Are there easier ways to do this" could be made more specific and generate better answers. – Voltage Spike Aug 3 '18 at 18:05
• @juan Fixed that. Imagine a board that sits on a table and is connected to the power supply, to the reset button and to the clock. It has many female sockets — "cells". You insert the "little pieces" into the "cells" to create a circuit (the little pieces communicate via light). This is not an actual game, this is my personal project I'm starting to work on. – decorator-factory Aug 3 '18 at 18:06
• @laptop2d Sorry for the Paint sketches, I have replaced those. I intended the first question to mean: "are there pre-made socket arrays with common pins that I can use to make this easier?". – decorator-factory Aug 3 '18 at 18:28

1) Are there easier ways to do this? Are there readily available sockets or designs for my purpose?

Connectors can be hard, usually searching a distributor like digikey in the connectors section is the best way to find the right connector. Another thing that might be valuable is to find a distributor catalog and look through it to get an idea of what's available.

Even a 2x2 0.1" header might be best for your purposes, or 4 seperate 0.1" headers. The real question is: do you want the connector to be the mechanical link, or a fastener?

3) How to choose the right R and C values for a given frequency?

RC filters form either low pass or high pass filters. High pass filters block DC, so only AC currents can pass through them. Filters block frequencies.

Either filter's cutoff frequency is at

$$cuttoff = \frac{1}{2\pi R C}$$

If I wanted to keep 10Hz and block everything over 100Hz then I'd make a low pass filter with a cutoff somewhere in between. Then I need to choose RC values, Lets say I have a 1k resistor, so I start there and solve for C, I'll try 20Hz. I get a C value of 0.8uF but those capcitors are hard to come by in a value like that so I round it to 1uF. Then I solve the cutoff for an R of 1k and a C of 1uf which would give me 15.9Hz then I decide if that would be acceptable for my requirements.

• Thanks! The 2x2 connector is an obvious solution, I was wondering if I could return to the polarised sockets solution with some fancy socket or if there already exist such big arrays/boards. – decorator-factory Aug 3 '18 at 18:52
• !Picture This-ish connectors might work as well if I applied some thought to the connections. – decorator-factory Aug 3 '18 at 18:57
• They have shrouded 2x2 0.1" headers (or simmilar) board to board that are polarized – Voltage Spike Aug 3 '18 at 19:03

I suggest you design a board consisting of polarised connectors, that is, connectors that can be plugged only one way in, and in this way detecting what orientation was the functional block inserted in isn't required.

I also suggest you feed each of these blocks with power (ie. 3.3V and GND pins) plus a set of signals to get all the blocks connected between them, using any communication protocol you like, such as CAN bus. Avoid expensive light communicating blocks.

It may even be easier/cheaper to make the motherboard be responsible of calculating the result of a certain pattern of connected blocks than to make the blocks themselves perform a particular task. In this scenario, an MCU/FPGA would detect what blocks have been connected and in which order and then output the simulated result.

• If I put a controller on every "little piece", its price might increase significantly, and it would require additional logic in the supply.I want the "little pieces" to be as dumb as possible. The pieces don't have to make good contact, and by "light communication" I mean an LED-photodiode communication. All the signals are 1-bit, and this is very convenient. An alternative design would be to just use a microcontroller and put some kind of serial identification chips on different components, but that could again increase the cost. – decorator-factory Aug 3 '18 at 18:40
• At first, I wanted to make polarised contacts that are basically three squares inside of each other and a circle in the center, but that would probably require a big PCB, and I said that in the question. By the way, most components don't even require a clock or reset signal, so they would just rectify the current. – decorator-factory Aug 3 '18 at 18:46

Figure 1. Pin header strips can be cut to length and used to make PCB connectors.

simulate this circuit – Schematic created using CircuitLab

Figure 2. Possible multi-orientation configurations. The plug-in board only needs one line of four pins that can pick up on any of the above.

The biggest concern with this arrangement is to prevent someone inserting with an offset of one pin and destroying your board. The simplest way of solving this might be to "key" one of the connections by using three pins and one socket on one side and three sockets and a pin on the other.