The control board is intended to be as modular and reconfigurable as possible, so that users can modify it to suit their particular design needs. This documentation will cover the fabrication and operation of a control board for pneumatic (air-operated) systems. The same guidelines will apply for a hydraulic (water-operated) control board, however it will need to use different components (discussed below).
The board consists of:
The base structure of the control board is a sheet of acrylic with a laser-cut "pegboard" design (the white board in the above image), which makes it easy to reconfigure, add, or remove board components. Most of the components are mounted to laser-cut acrylic parts (the red pieces in the above image) which help to organize the board and also make reconfiguring the system easier.
On the next page, we discuss some options and alternatives for modifying the board to best suit your needs.
The choice of operating fluid largely depends on your application. Water and air each have their own advantages and disadvantages as an operating fluid. For example, a pneumatic system can draw air from the environment (so the system doesn't need a reservoir) and any leaks that occur will not cause a mess. However, air is a compressible fluid and this can mean that it takes more energy for the pump to compress the air to reach the desired pressure. Furthermore, for some medical applications, particularly when an actuator will interact with blood, using air presents serious safety concerns.
The opposite is true for hydraulic systems: they require a reservoir and leaks will result in water spillage which may cause problems, but the system may be more energy efficient and water may be a safer choice for some applications.
As mentioned on the previous page, we describe a pneumatic control board here but it is relatively straightforward to use these instructions to build a hydraulic board. The main difference to consider is the selection of components. The following items on the Bill of Materials should be changed if you want to build a hydraulic control board (in most cases the vendors offer hydraulic versions of these parts):
All other parts of the control board should stay the same, and the general fabrication and operation instructions provided here should apply.
Most of the components on the board (and the particular models and brands of each component) can be replaced with alternatives based on cost, availability, and performance. We have found parts and suppliers specified here to be easy to obtain in the United States, but there may be better local options in other parts of the world. The part specification we provide can be useful in finding alternative components. We strongly advise you to get in touch with vendors directly to discuss your particular needs; most vendors can provide design expertise in their area and this can save you a lot of time and money.
Here we discuss some particular alternatives, but this list is by no means exhaustive:
As mentioned above, the current design uses MOSFETs to control the switching of the solenoid valves. This setup makes it possible to use pulse width modulation (PWM) to control the pressure of the fluid passing through these valves. During PWM, high-frequency pulses are sent to the solenoid valves, opening and closing them rapidly. By varying the length of these pulses, the amount of time the valve is open or closed is adjusted, and therefore the output pressure is adjusted.
The drawback of using PWM on the control board is that it is less straightforward to set up. For beginners with relatively little electronics and programming experience, this is not the easiest method to start with. The other option for pressure control is to use a pressure regulator. While being easier to use, pressure regulators can be expensive and allow for less control of the system. Using a single regulator allows you to vary the pressure of the whole system, but if you want different pressure in different parts of the system (e.g. different pressures for different actuators) then you need a way to control the pressure at each valve. PWM has the advantage that each valve is individually addressable, which solves this problem. However if that isn't a problem for your system, then a pressure regulator might make sense.
Sensors can easily be added to or removed from the board without affecting its performance. The choice of sensors again depends on what types of applications you are interested in.