RDB G 001
Generic pages: | Introduction | Naming convention | Main Interfaces | Feature Interfaces | Steppers Interfaces | RDB_calibrations | RDB_DIY_tips |
Specific pages: | RDB_G_001 |
Contents
Features Overview
This board in combination with a development board and stepper drivers, should provide all needed electronics for basic functioning of a reprap printer:
-Voltage regulators: 2 (adjustable)
-Endstop headers: 3
-Thermistor headers: 5
-Switches: 4xVdc & 1xVac(optional)
-Pcb size: ~ 10x10 cm
-DIY-able: format and traces "bulky" enough so board could be made with any technique
Stepper drivers
Stepper drivers are to be driven with step/dir/en lines taken directly from GPIO of microcontroller to the driver boards. Hence such lines are not a part of this board, and are of no concern for this board.
Power input
- simple reverse polarity protection with high current diode and fuse
- transient supressor
- max input voltage depends on the regulators used, e.g.
Voltage regulators
- two adjustable voltage regulators, in paralel configuration
- voltage regulators are 3 terminal type, TO-220 package, e.g.: LM317 LM1086, and similar pinout compatibility
- adjustment pots are multiturn
- first regulator purposed usage for development board supply, has 2 outputs, no further connections on the board
- second regulator for TTL voltage, has 2 outputs, and is further connected VCC points on the board
Thermistors
Thermistors ADC pins come from development board and further go to thermistors physical location.
Endstops and others
Endstops pins just pass through the board to offer headers coupled with vcc and gnd of the board, to go to endstops physical location. Similar composition can be used for other pins, this may come in handy for some communications sniffing and such.
Switches
All switching components are to-220 package, 3 terminal, with heatsink space for standard radiators and are placed in line for common backplate type with 2 points fixture. All switches use their own ground/connection paths and are not connected to the board's input ground.
FET Switches (vdc)
- 2 low side switches, fets with series fuses sockets, presumed for high current
- 2 low side switches, fets without fuses
Truth table: feature active when high
| TTL signal | Behavior |
|---|---|
| high | conducting |
| low | non-conducting |
The fets leds are kind of counter-intuitive, because are linked in paralel to the mosfet. So leds are off when fet is conducting. If there is a load connected, when the mosfet is not conducting the voltage rises and the leds switch on. The fets have some optional micro-snubbers, mostly because needed to leave space for standard to-220 radiator "hat". Normally snubbers need to be tweaked and then tested a lot in order to make them effective, but on the other hand the default values should provide "something", and it cant hurt, to say so.
Triac Switch (vac)
- 1 (optional) zero-crossing optocoupler commanding a triac for on-off control of one Vac line
Truth table: connected to transistor's base, feature active high
| TTL signal | Behavior |
|---|---|
| high | conducting |
| low | non-conducting |
Truth table: directly connected to optocoupler, feature active low (inverted)
| TTL signal | Behavior |
|---|---|
| high | non-conducting |
| low | conducting |
Triac is optional, for ac switching. It can be used to switch some spindle motor, or if the bed is supplied with ac. This is on-off control only (not proportional).
Mains voltages are dangerous, so use this with care and wisdom. Ensure minimal distances and good isolation of the board where the mains circuit is located. Ensure no shorts can possibly occur anywhere: shorting 230vac to 5vdc isnt pretty. Be warned.
Triac by default uses an zero crossing optocoupler, for better switching, so its max switching speed depends on the AC frequency. Triac should be snubberless type (not needing snubber). Unlike fets leds, triac led is normal, e.g. led is on when triac is on and vice-versa.
The TTL command signal can be tied in two ways in the 2 wire connector. If connected to the base of the transistor, this will conduct the line to ground, so triac will be active when the the TTL signal is high. If connected to the drive line directly, it will sink the current into the uC GPIO itself, so the triac will be active when the TTL signal is low. So, second mode of operation is inverted of the first (feature enabled when low and disabled when high).
Requirements fot DIY
Ability to produce the boards either with toner or photo transfers, or with pcb milling. Soldering capability and accessories. Multimeter is mandatory for adjustments of voltage regulators (and perhaps temperature reading multimeter for thermistor temperature calibrations).
