Arduino Hat Design Inquiry
Worked for 4 mins 2 sec
Part selection is underway. I found a PN532 RFID IC and a 5 V relay with verified 120 VAC-capable contacts; the wide-input buck IC search needs a library fallback because the first pass only found module-style entries.
Worked for 4 mins 32 sec
Main ICs are added. I’m now adding the required passives and will wire power, SPI level shifting, microSD, relay driver, and safe relay contact terminals.
Worked for 6 mins 32 sec
I started the fully integrated Arduino Uno shield schematic and renamed the project to Arduino RFID SD Relay Shield.
Completed:
- Added PN532 RFID IC, microSD socket, relay, relay driver, flyback diode, MP1584 buck, 3.3 V LDO, SPI level shifter, terminal blocks, Arduino header placeholders, and support passives.
- Wired the initial 28 V input, 5 V rail, 3.3 V rail, SPI level-shift path, relay driver, and relay contacts.
- Created:
Important: the schematic is not layout-ready yet. Review still reports unresolved floating pins, mainly because the MP1584 buck support network and PN532 crystal/antenna/matching/reset circuitry need to be completed from the datasheets before moving to PCB layout.
Complete missing circuits
Fix ERC warnings
Improve Arduino headers
Add protection features
Prepare for layout
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Board Bring-Up Plan — Arduino RFID SD Relay Shield
Prerequisites
- Equipment: current-limited bench supply, multimeter, oscilloscope or logic analyzer, Arduino Uno, known-good 13.56 MHz RFID tag, known-good microSD card, isolated test load for relay contacts.
- Safety: do not connect 120 VAC until low-voltage power rails, relay control, and PCB isolation spacing have passed inspection.
1. Visual Inspection
- Check orientation of U_BUCK, U_LDO, U_LVL, U_RFID, Q1, D_FLY, K1, J_IN, J_RELAY, and J_SD.
- Verify no solder bridges around U_RFID QFN pins and exposed pad.
- Verify relay contact copper is isolated from low-voltage logic copper.
2. Power Rail Verification
Table
| Rail | Source | Expected Voltage | Measure At | Current Limit | Pass Criteria |
|---|---|---|---|---|---|
| VIN_28V | J_IN | 28 VDC nominal | J_IN:1 to GND | 250 mA initial | No excessive input current |
| 5V | U_BUCK output | 5.0 V | C_BUCK_OUT:P1 to GND | 300 mA initial | 4.75–5.25 V, no overheating |
| 3V3 | U_LDO output | 3.3 V | C_LDO_OUT:P1 to GND | 150 mA initial | 3.20–3.40 V |
Procedure:
- With power off, measure resistance from VIN_28V, 5V, and 3V3 to GND.
- Apply 28 V with current limit set low.
- Verify 5V before inserting the Arduino Uno.
- Verify 3V3 before testing RFID or microSD.
- Check buck ripple on 5V and LDO output ripple on 3V3.
3. Critical Signals
Table
| Signal | Net | Expected State |
|---|---|---|
| Relay drive | ARD_D7_RELAY | Low at reset; high energizes K1 |
| SPI clock | SPI_SCK_3V3 | 0–3.3 V clock during SPI transactions |
| SPI MOSI | SPI_MOSI_3V3 | 0–3.3 V data from Arduino through U_LVL |
| SPI MISO | ARD_D12_MISO | 0–3.3 V data to Arduino |
| SD CS | SD_CS_3V3 | High when microSD deselected |
| RFID CS | RFID_CS_3V3 | High when PN532 deselected |
4. Functional Validation
Table
| Test | Components | Expected Result |
|---|---|---|
| Arduino power from shield | J_IN, U_BUCK, Arduino headers | Arduino powers reliably from 5V rail |
| microSD SPI init | U_LVL, J_SD | Card initializes and file read/write succeeds |
| PN532 detect | U_RFID, antenna network | RFID tag UID read succeeds |
| Relay GPIO test | Q1, K1, D_FLY | Relay actuates only when commanded |
| Relay contact continuity | K1, J_RELAY | COM switches from NC to NO when coil is driven |
5. Open Bring-Up Blockers
- MP1584 buck peripheral network is not finalized yet.
- PN532 crystal/antenna/matching/reset networks are not finalized yet.
- ERC currently has unresolved floating-pin warnings; do not proceed to layout/manufacture until fixed.
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