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PRODUCTS
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Teleo Modules |
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Teleo Modules
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TELEO MODULES |
The heart of a Teleo System is its modules. This section aims to provide a general overview of Teleo modules.
Each module has approximately the same design. It is supplied as a raw circuit board mounted 1/4" off an ABS base which is drilled for mounting into the user's project. The user can also chose to mount the board directly without the base if space is a concern. See the Physical Dimensions section for details.
Electronically, the main feature of the board is the microprocessor, which performs all the computational work of the board. Also on present are
- a power regulator and associated components for creating the 5V supply required by the processor
- a crystal which the processor needs to co-ordinate its internal processes. Note that the processor has a clock quadrupler which allows it to run at 40MHz with only a 10MHz crystal.
- an RS-485 driver chip to permit communication on the network.
Beyond these, the boards have whatever electronics they require to perform their function. Almost all modules have connectors for wiring-up external circuitry.
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| Teleo MultiIO Module |
Each module has a push button and an LED which together provide a few simple functions. When a module is first powered-up, the LED flashes for a second, then signals normal operation by flashing very briefly once a second. The LED also indicates incoming and outgoing data with brief flashes.
The push button is used to identify a module to the controlling software. When pushed, a button-press message with the module's address is sent to the controller.
The push button is also used to prepare the module to receive a new address. This is achieved by holding the button down for 3 seconds. When this happens, the LED flashes very quickly to confirm. The module returns to normal when it receives an Address Set message or the button is pushed again.
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Push Button and LED |
The network connector is the means by which the module is powered and can send and receive data to and from the network.
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| Network Connector |
Each module has its own microprocessor. This processor handles all the network communication along with whatever else it is designed to do as the brains of each particular module.
We mostly use Microchip's (http://www.microchip.com) PIC18 series microprocessors which run at 40MHz. They execute most instructions every 4 clock cycles yielding an operating speed of almost 10 million instructions a second (MIPS). They are programmed in C with HiTech's PICC-18 compiler (http://www.htsoft.com).
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PIC18 Microprocessor |
The microprocessor can't generate the special differential signals needed for communicating on the Teleo Network. An additional RS-485 driver chip is required to do this. We use the Maxim MAX483.
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RS-485 Driver |
An additional advantage of the presence of this chip is that it protects the microprocessor from incorrect voltages on the network data lines which might happen if a network cable is wired incorrectly or if the some of the lines on a Teleo module are shorted.
The electronics on most modules requires +5V in order to function correctly. Since the network's V+ line provides a greater voltage (7.5V - 30V), a power regulator must be used to reduce this to the 5V required. We use a 7805 variant.
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Power Regulator |
The regulator can run quite warm if the 5V circuit is being used to power circuitry beyond the basic module electronics. A heatsink can be added if the regulator gets more than a little warm, although since this is often a good indicator of something going wrong make sure you check the circuitry closely. The regulator will shut down automatically if it gets too hot. Monitor the regulator temperature particularly if a higher voltage (i.e. >12V) is being used.
The In-Circuit Programming (ICP) Connector, shown below, provides the electrical connection to reprogram and develop new code on the the module's microprocessor.
ICD ConnectorSeveral of the modules use MOSFET switches to be able to switch larger currents and voltages than the microprocessor can by itself. MOSFETs are a special kind of transistor with the feature that they require very little current to switch much larger currents and have a very low resistance when switched on.
The MOSFET mostly used on Teleo boards is the IRLD024 from International Recifier (http://www.irf.com). This device has a maximum voltage of 60V and an on resistance of (0.1
). It can switch up to 2.5A continuously if held at 25 degrees C. We prefer to say that they can switch 2A to be conservative. If they are made to conduct more current than their rated limit (which they will do very readily) they will quickly heat up. If they get too hot they will ultimately be destroyed. They are socketed in our designs so that they can be easily replaced in case they are damaged.
MOSFET SwitchTransient Voltage Suppressor (TVS)
Transient Voltage Suppressors (TVSs) are put on some of the Teleo modules to provide protection for inputs against accidental miswiring. They operate like giant zener diodes: connecting between an input on a sensitive device (in this case, our microprocessor) and ground. Under normal circumstances they don't influence the circuit at all, but if a large voltage appears on the input line (whether from a static discharge or miswiring) they quickly become excellent conductors and they pass the harmful voltage directly through to ground, preventing it from going further and damaging the input of the microprocessor.
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TVS |
Some modules with potential for large current consumption have a built-in mechanism to limit the current being drawn from the network. This fuse-like device, called a polyswitch, permits amounts of current to flow through it up to a certain maximum limit. When this current limit is exceeded, the material in the device changes from its conductive form into a crystaline, non-conductive form breaking the circuit. When the load is removed, the material cools down and reverts to its conductive form allowing the system to function as normal.
The polyswitch shown here is mounted under the circuit board in order to avoid making the board higher than necessary and to avoid people refering to it as "the handle".
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Polyswitch |
Many of the Teleo Modules use screw connectors. These are a very convenient way to permit the attachment of raw wire to the board without requiring soldering or crimping.
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Screw Terminals |
The insulation on the wire should be stripped back around 1/8" and the strands of wire twisted gently together to prevent them from separating. Then the wire should be inserted into the terminal and the terminal tightened. If it is anticipated that the wire might be inserted and removed a number of times, tinning the wire will increase its longevity. Tinning is the process of applying solder to metal - usually to make it easier to solder two parts together although in this case more to increase the wire's strength and rigidity.
Correct WiringDepending on the gauge of the wire, and the dexterity of the user, more than one wire can sometimes be accomodated in these terminals. However sometimes a more robust approach may be required.
Ad Hoc Connector Many modules have a V+ terminal. This is connected to the Teleo Network's V+ line and therefore has the same voltage as the main network power supply. In some modules, the V+ terminal might be protected by a polyswitch.
The V+ terminal can supply enough power to run many things; lights, motors, valves, sirens, etc.
Many modules have a 5V terminal. This is 5V provided by the module's on-board regulator and should be used only for very light loads (<100milliamps, ideally) like sensors, potentiometers, etc. This 5V is the same supply that the processor uses, so it can't be attached to electrically noisy things unless filtering is provided.
When using the 5V supply, be sure to monitor the regulator's temperature - it's OK if it is warm, but if it's too hot it will shutdown. Currents of more than 100mA, particularly at higher voltages may necessitate a heatsink on the regulator.
Connected to the system's ground line. Mostly used for sensors and other input devices, although can also provide a ground point for connecting external power supplies.
Many modules share a need for a simple digital input. This input will provide the microprocessor with a "1" or a "0" depending on the state of the switch circuit or device. The circuit diagram below shows the input circuit mostly used.
Digital In Circuit Diagram The idea is that the switch is connected to the appropriate terminal. When it is closed, the DIn pin on the microprocessor is brought to 0V. When it is open, the pull-up resistor makes sure that the DIn pin reads 5V. On some of it's pins the PIC18 microprocessor has the pull-up resistors built-in to the processor itself, so extra components are not needed on the board.
Notice that when the switch is closed, the input pin will read 0V - (0). When the switch is open, the pull-up resistor brings the line up to 5V - (1). Although this is not normally the way we think about switches and buttons, this kind of inversion is very common in electronics. If necessary, the microprocessor can invert the signal again so that it comes out the right way.
To protect against voltages higher than 5V applied to the input pin, most digital inputs are protected by a TVS. The TVS doesn't influence the circuit at all when the voltages on the terminal are between 0 and 5V, but when the voltage is outside that range it begins conducting, preventing the microprocessor from being damaged.
One of the main features of several Teleo Modules is their ability to be able to control loads with much higher currents than is possible with the raw output of the microprocessor alone. Digital Out circuits need to be able to switch the load on and off by changing the value they output between 1 and 0. PWM circuits need to do exactly the same thing, except they turn the output on and off thousands of times a second to achieve the effect of a variable voltage. If the load is a light, for example, If the line is on longer than it's off each cycle, the light will look brighter, if the line is off longer than it's on it will look dimmer. The output circuit used for both uses is shown below.
Digital Out / PWM Circuit Diagram The MOSFET mostly used on Teleo boards is the IRLD024 (the "L" is for logic level) from International Recifier (http://www.irf.com). The maximum voltage the device is rated to handle is 60V, and the maximum current is 2.5A if the device is kept at 25°C. Toward the upper end of it's range (i.e. >1.5A), the device may start to get warm. Watch for this and be prepared to add some kind of heatsink to the device if necessary.
When the microprocessor switches its output from 0 (0V) to 1 (5V), the MOSFET switches on and starts conducting. Note that for 5V to switch the gate, the MOSFET used must be a logic level device since MOSFET's usually require a 12V Gate voltage.
Once the MOSFET is conducting, the load on the output gets a connection to ground and current begins to flow. The load itself must not exceed the 2A's the MOSFET can switch. The resistance of the MOSFET is around 0.1
The output is arranged this way, with the switch on the low-side of the load, so that the drain (D) of the MOSFET can connect to the load and the load can connect to a wide range of different voltages, not limited to 5V or the V+ of the Teleo Network.
Many Teleo Modules have a requirement for analog inputs to read sensors, potentiometers, and so on. The Analog In circuit used in most cases is shown below.
Analog In Circuit Diagram The sensor provides a voltage between 0 and 5V which is read by the Analog Input and converted into a 10b number (0 - 1023). Each level is therefore 5V / 1024 which is about 0.0049V. Internally the microprocessor re-ranges this number as it needs to.
The TVS is provided as a safety mechanism to guard against the accidental connection of a voltage outside the range 0 - 5V. Like most pins of most chips, the analog input pins can not withstand the direct application of voltages greater than their supply.
The high value pull-down resistor tends to hold unused inputs at 0V (or very close). Without this, unused inputs would report random values.
Teleo modules were designed to be built into other people's projects.
They are shipped with 1/4" Black ABS bases to offer some protection while the boards are being experimented with. The boards can be mounted via the bases or the bases may be removed and the boards mounted directly.
Most of the functional modules share the same basic printed circuit board (pcb) and base layout.
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Dimensions Base Board and PCB |
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