Timer

CYTM V5 Digital Timer PCB

24 VDC cyclic relay timer board for the firmware in ../Final/5-26.c (MG51FB9AE, unchanged pin map). 2-layer, 50 x 80 mm, display/LEDs/keys/terminal on the front, everything else on the back.

Status: prototype (Rev A). ERC 0 errors / 0 warnings, DRC 0 violations, 0 unconnected, schematic parity clean.

Rebuild

Everything is generated from scripts/circuit.py (parts, nets, placement). One command rebuilds and checks it all:

python scripts/build.py

Needs: KiCad 10 (C:\Program Files\KiCad\10.0), Python 3.10+ with PyMuPDF, Java 17, and tools/freerouting-1.9.0.jar (not in git; get it with gh release download v1.9.0 -R freerouting/freerouting -p freerouting-1.9.0.jar -D hardware/tools). scripts/env.py holds the paths. Takes about 4 minutes, most of it autorouting and 3D renders.

Freerouting does not give the same tracks on every run. build.py only reports BUILD OK when the new board passes every test, ERC and DRC, so any accepted run is clean; the files in output/ belong to the last run.

Outputs (output/)

• gerbers.zip: Gerber X2 (both copper, mask, paste, legend, outline) + Excellon drill. Upload to the PCB maker.
• bom.csv: parts grouped by value and footprint.
• positions.csv: pick-and-place, mm, origin at the board's bottom-left corner.
• schematic.pdf
• render_top.png, render_bottom.png, render_iso.png
• films_panel_3x2.pdf: 1:1 films, 3 x 2 panel, one page per layer (back layers mirrored, mask negative). Check the 10 mm scale bar after printing.

Circuit summary

• 24 V in: SMBJ28CA bidirectional TVS on the raw input, then SS36 (60 V) reverse-polarity diode, 100 uF bulk, L78M05 (DPAK) to 5 V.
• Relay: SRD-24VDC-SL-C, 24 V coil from the protected rail, MMBTA06 driver (80 V), 1N4148W flyback. COM is fed from raw IN+ so load current bypasses the diode. IN+ -> COM, NO -> OUT+ and IN- <-> OUT- are 3 mm tracks (5 A).
• Display: 3-digit 0.56" common anode (BA56-12EWA pinout). Each digit and the LED group is driven by an SS8050 emitter follower, so "pin high = digit on" (firmware polarity) and the digit pins carry only base current. The 8 segment pins each sink their segment current through 330 ohm (~4.5-6 mA peak).
• The 3 mm load tracks are not tinned (no mask opening): they run under the terminal and relay bodies. 3 mm of 1 oz copper carries 5 A at about 10 C rise.
• LEDs on the LED group (P0.6): SEC = seg A, ON/OFF = seg B (relay on), MIN = seg C, SET = seg F (setting mode).
• Keys to GND: SET P1.7, START P2.0 (10k pull-up), STOP P3.0.
• ICP header J2: 1 VDD, 2 ICE_DAT (P1.6), 3 ICE_CLK (P0.2), 4 nRST (P2.0), 5 GND.

Before ordering in volume

1. MCU pinout. The MG51FB9AE symbol assumes the N76E003 / MS51FB9AE TSSOP-20 pinout (scripts/gen_symlib.py, checked by tests/test_libs.py). Confirm it against the Nuvoton MG51 datasheet.
2. Display. Pinout taken from Kingbright CA56-12 with pin 6 not connected (3-digit BA56-12EWA, 37.8 x 19 mm). Confirm the part you buy uses the same 12-pin layout.
3. Enclosure. Board size, display, key, LED, hole and terminal positions are assumptions. Measure the enclosure and change the coordinates in scripts/circuit.py, then run build.py.
4. Firmware. The SEC and MIN LEDs are wired (seg A / seg C in the LED-group slot) but the current firmware does not light them. ON/OFF and SET already work.
5. Relay rating. The tracks carry 5 A. The SRD relay is rated 10 A, but the terminal block and board are not.
6. Surges. The L78M05 is rated 35 V; the SMBJ28CA clamps up to 45 V on a full-energy surge. For harsh supplies use a 40 V+ regulator (or a small buck converter) in the same position.
7. Prototype checks. Measure the regulator tab temperature (about 0.9 W at 24 V) and the display brightness (330 ohm gives about 1.2-1.5 mA average per segment; 220 ohm is brighter but heats the regulator more).
8. Inductive loads. For valves or contactor coils on OUT, fit a freewheel diode at the load.