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A Nokia 5110/3310 PCD8544 breakout module can be connected to a Raspberry Pi Pico over SPI with power, three control lines, two SPI lines, and an optional backlight connection. One practical SPI0 assignment is VCC to 3V3, GND to GND, DIN to GP19, CLK to GP18, D/C to GP20, RST to GP21, CE/CS to GP17, and BL/LED to GP22. That pinout is an example, not a universal standard: check the labels on your particular module and the GPIO layout of your Pico board first.
The original LCD and keypad removed from a Nokia 3310 are different projects. The handset LCD uses a device-specific connector with a listed 2.8 V supply, while the keypad is a row-and-column switch matrix whose connector mapping is not established by a generic breakout diagram. Identify the exact parts before applying power.
First identify the Nokia hardware you have
“Nokia 3310 display” can mean either a modern breakout board sold for hobby projects or the bare LCD removed from an original phone. They do not share a safe, interchangeable wiring map.
| Part | What the documentation establishes | Best Pico approach |
|---|---|---|
| PCD8544 5110/3310 breakout | Exposes power, SPI data and clock, chip select, data/command, reset, and often a backlight pin. | Use the module silkscreen and its electrical specifications, then adapt the example SPI0 map below. |
| Bare original handset LCD | A connector reference lists reset, VOUT, ground, chip select, control/data, serial data, serial clock, and a 2.8 V supply. | Obtain the exact LCD pinout and voltage requirements. Do not copy the breakout wiring. |
| Original 3310 keypad | Keys are switches arranged as a row-and-column matrix; a complete Pico-ready connector map is not established. | Trace the contacts on your exact keypad with its documentation or a continuity meter, then assign rows and columns to GPIOs. |
Look for “PCD8544” or “Nokia 5110/3310” on a breakout board. Pin names vary: DIN may be labeled DATA or MOSI, CLK may be SCLK, CE may be CS or SCE, D/C may be DC, and BL may be LED. Match the function rather than the spelling.
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A Pico’s GP numbers are GPIO identifiers. They are not the same as the physical pin numbers around the header. For example, a wire going to GP19 must be located using the board’s official pinout, not by counting to the nineteenth header position. Confirm the exact Pico-series board variant before inserting wires.
Parts and checks before connecting anything
- Raspberry Pi Pico or a compatible Pico-series board with its pinout available.
- A PCD8544 breakout module, if you are using the hobby-board route.
- Male-to-female jumper wires and a breadboard for temporary wiring.
- A USB cable and a development environment that supports your chosen Pico firmware and PCD8544 driver.
- A multimeter with continuity mode if you are tracing an original keypad or bare handset LCD.
Read the display board’s voltage markings before connecting its VCC. The example below uses the Pico’s 3V3 rail because that is the documented assignment for the cited PCD8544 Pico example. Never assume that a board labeled only “LCD” accepts 5 V, and never apply the example to a bare phone LCD without its own electrical documentation.
Inspect the breakout’s header orientation and silkscreen under good light. Some boards place VCC at one end and others reverse the order; a table copied from another listing is not enough. Check for solder bridges, bent header pins, and a backlight jumper or resistor if the board has one. Keep the Pico disconnected from USB during every rewiring step.
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Recommended wiring for a PCD8544 breakout
The following is a workable SPI0 example for a common Nokia 5110/3310-style module. It is a starting point for configuration, not a mandatory Pico pin map.
| Display-module label | Pico connection | Purpose |
|---|---|---|
| VCC | 3V3 | Module supply in this example |
| GND | Any Pico GND pin | Common reference |
| DIN | GP19 | Serial data; SPI0 transmit in the cited example |
| CLK | GP18 | Serial clock; SPI0 clock in the cited example |
| D/C | GP20 | Selects command or display-data bytes |
| RST | GP21 | Hardware reset |
| CE, CS, or SCE | GP17 | Chip-select line |
| BL or LED | GP22 | Backlight control in this example |
Some modules omit the backlight connection, expose LED through a resistor, or expect the backlight to be tied to a supply instead of switched by a GPIO. If your board has no BL/LED pin, leave that row out. If it has additional pins, consult that board’s documentation rather than guessing.
Wire the power and ground first
- With the Pico disconnected from USB, connect the module’s GND to a Pico GND pin.
- Connect VCC to the Pico 3V3 rail only when the module documentation calls for that supply.
- Check that no jumper accidentally bridges VCC and GND or touches a neighboring header pin.
- Verify the connector is seated in the intended breadboard rows; a one-column offset can put power on a signal pin.
Add the SPI and control lines
- Connect DIN to GP19 and CLK to GP18 for the example SPI0 arrangement.
- Connect CE/CS to GP17, D/C to GP20, and RST to GP21.
- Connect BL/LED to GP22 only if you want firmware-controlled backlight. Follow the module documentation if the LED input requires a resistor, a separate supply, or a different logic arrangement.
- Compare every wire against the module’s printed labels and the Pico’s official GPIO diagram before powering the board.
You may choose different free GPIOs, but then change the software configuration to match. The important relationships are the SPI clock and data pair plus three independent control signals. Do not assume that a library example written for a Raspberry Pi computer uses the same physical pins as a Pico; the Adafruit wiring example demonstrates signal roles, while the Pico example supplies this particular GP-number assignment.
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Configure the display in software
The wiring works only when the driver uses the same pins. In MicroPython, the Pico C SDK, Kaluma, or another PCD8544-capable environment, select SPI0 and configure:
- clock: GP18
- transmit/data output: GP19
- chip select: GP17
- data/command: GP20
- reset: GP21
- optional backlight output: GP22
The Kaluma PCD8544 example documents this Pico SPI0 assignment; official Pico documentation explains GPIO naming and alternate functions. Other libraries may call the same signals MOSI, SCLK, SCE, DC, and RST. Set the library’s names to the physical functions above rather than copying an example written for a different Raspberry Pi computer.
Keep the display geometry and controller selection aligned with the actual module. A board sold as a Nokia 5110/3310 display normally identifies the PCD8544 family, but a generic monochrome LCD listing may use a different controller. If initialization succeeds electrically but the screen remains blank, check the driver target before changing wires.
Use a staged test
- Start with the display disconnected from USB while you recheck power polarity and GPIO numbers.
- Run the driver’s simplest initialization and clear-screen routine. A successful initialization should release reset and send commands without a wiring error.
- Draw a solid pattern or a border before attempting a larger user interface. This makes missing rows, swapped data and clock lines, and contrast problems easier to distinguish.
- Test text or graphics only after a simple pattern is reliable.
- Only after the display is stable should you enable the backlight and add keypad scanning.
A blank screen is not automatically a dead LCD. It can indicate reversed power, a wrong controller selection, swapped DIN and CLK, an incorrect chip-select or D/C pin, reset held in the wrong state, or a contrast setting unsuitable for that module. Change one variable at a time and record each change so a working combination is not lost.
Why the original handset LCD needs a separate plan
An original 3310 LCD connector is not a convenient version of the breakout header. The handset connector reference identifies reset, VOUT, ground, chip select, control/data, serial data, serial clock, and a 2.8 V supply. Those names describe the phone’s connector context, not a guaranteed Pico wiring recipe.
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- Do not assume the 2.8 V supply requirement is interchangeable with a 3.3 V module rail.
- Confirm whether the LCD needs regulated power, level translation, or additional bias circuitry before connecting Pico GPIOs.
- Identify the connector orientation and pin numbering from the exact LCD or phone board; connector diagrams are orientation-sensitive.
- Check whether VOUT is an internally generated bias node rather than an ordinary supply connection; do not attach it to a Pico rail without the device specification.
If you cannot obtain a reliable pinout and voltage specification for the handset part, the PCD8544 breakout is the safer route. It exposes the signals in a form intended for hobby wiring and avoids the phone’s undocumented mechanical and electrical details. A bare LCD may also require a custom adapter or fine-pitch connector, so the electrical identification problem comes before software.
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How the original 3310 keypad works
The handset keypad does not provide one independent digital wire per key. Its button contacts form a matrix. A key press electrically joins one row line to one column line, and firmware determines the pressed key from that intersection.
Trace your exact connector
- Disconnect the keypad completely from the Pico and any power source.
- Obtain the keypad assembly’s schematic if one exists. Do not substitute a schematic for a different Nokia model; matrix labels and connector order vary.
- Set a multimeter to continuity or resistance mode. Press and hold one key while probing pairs of connector contacts.
- Record which two contacts close for that key. Repeat for every key and organize the results as row-versus-column intersections.
- Look for contacts that recur across several keys; these are likely common row or column lines. Confirm the pattern with additional keys instead of inferring it from one measurement.
- Mark the connector orientation and make a pin map before attaching any Pico wire.
- Photograph or label the connector so the map still makes sense after the keypad is removed from the workbench.
A teardown of the 3310 establishes the row/column principle, but it does not establish a complete connector-to-GPIO map for every keypad assembly. A schematic for another Nokia handset can demonstrate why labels differ, but it cannot be used as the 3310 pinout. Even two assemblies sold for the same phone can have different flex-cable orientation or contact numbering, so continuity results from your own part are the final check.
Connect the matrix to GPIOs
After you know the contacts, assign each row and column to a free Pico GPIO. Firmware normally drives one group in turn and reads the other group, then translates the detected intersection into a key name. Whether rows are outputs and columns are inputs, which pull resistors are used, and whether the lines are active-high or active-low depend on your circuit and firmware design.
- Keep a written map such as “row 2 + column 4 = 5” beside the code.
- Configure unused lines so they do not float while a scan is in progress.
- Debounce each key in software; a physical press can produce several rapid transitions.
- Scan one row or column at a time and allow a short settling interval before reading the opposite group.
- Never drive two opposing matrix lines to conflicting fixed levels at the same time.
- Test a single key while watching the raw row and column readings before adding key-repeat or menu logic.
If a key appears permanently pressed, first disconnect the matrix and check for a short between its two contacts. If all keys are wrong in a consistent pattern, suspect connector orientation or a row/column order error rather than debounce timing. If only one key is unreliable, inspect that contact and its flex cable for contamination or mechanical damage.
If the project does not require the original handset keypad, a separate matrix keypad is simpler. Choose one with an explicit row/column connector diagram and include those labels in your wiring notes. No particular generic keypad model is required for this project; the advantage is that its connector and matrix dimensions are documented from the start.
Combining display and keypad GPIO assignments
The display example uses GP17 through GP22, leaving other GPIOs available for a keypad, but the exact free pins depend on your Pico board, other peripherals, and the matrix size. Keep the display’s SPI clock and data lines dedicated to SPI0, then allocate enough additional GPIOs for every distinct keypad row and column. Count matrix lines, not keys: a matrix with several keys may need far fewer GPIOs than one wire per button, but its scan code must know every intersection.
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| Design choice | Advantages | Risks or work required |
|---|---|---|
| PCD8544 breakout plus separate matrix keypad | Documented module signals and a clearly labeled keypad make troubleshooting straightforward. | Requires an additional keypad and enough GPIOs. |
| PCD8544 breakout plus original 3310 keypad | Preserves the handset’s buttons while using the easier display interface. | Requires continuity tracing and a custom matrix map. |
| Original LCD plus original keypad | Retains the phone’s original hardware. | Both the 2.8 V display interface and keypad connector are device-specific; documentation and electrical verification are essential. |
For a first build, the breakout-plus-separate-keypad route minimizes unknowns. The mixed route—breakout display with the original keypad—preserves the handset feel while limiting the display work to a documented PCD8544 interface. Reusing both original parts is possible only after their connector, voltage, and matrix details are established individually.
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Troubleshooting by symptom
| Symptom | Likely checks |
|---|---|
| No backlight | Verify that the module actually has a BL/LED pin, that GP22 is configured as an output, and that the board does not require a resistor or separate backlight supply. |
| Backlight works but no pixels appear | Check VCC and GND, controller selection, reset, D/C, chip select, and the SPI data/clock assignments. Confirm the library is targeting a PCD8544 display. |
| Random or garbled pixels | Look for swapped DIN and CLK, loose breadboard contacts, an incorrect SPI peripheral, long jumper wires, or a floating control line. |
| Only part of the screen updates | Inspect the display initialization and contrast configuration, then test a full-screen pattern. A partial pattern can also expose a driver geometry mismatch. |
| Every keypad press reads the same key | Recheck the row/column map, connector orientation, and the scan routine’s active levels. Verify each contact with a continuity meter. |
| Several keys appear pressed together | Check for matrix lines driven at conflicting levels, missing pull resistors, shorts on the connector, or software that scans more than one row at once. |
| Pico resets when the display or backlight starts | Disconnect power, inspect for a VCC-to-GND fault, and verify that the module’s current and voltage requirements are compatible with the Pico rail. |
| Display works until the keypad is connected | Remove the keypad, restore the known-good display test, then add one traced matrix line at a time. A misidentified keypad contact can short a GPIO or a supply line. |
A safe bring-up sequence
- Identify whether the display is a PCD8544 breakout or a bare handset LCD.
- Write down the module’s exact labels, supply requirement, and connector orientation.
- Wire only VCC and GND, with the Pico unpowered while you inspect the circuit.
- Add DIN, CLK, CE/CS, D/C, and RST according to the selected map.
- Configure the matching SPI peripheral and GPIO numbers in software.
- Run a minimal display test before attaching a keypad.
- For an original keypad, map every contact with continuity testing and document the matrix.
- Connect rows and columns to unused GPIOs, implement a one-line-at-a-time scan, and add debouncing.
- Test one known key at a time, then test combinations only after single-key readings are reliable.
- Save the final wiring diagram and pin map with the code so a future rebuild does not depend on memory.
This sequence separates power and display faults from keypad-mapping faults. It also prevents a connector diagram for one Nokia component from being mistaken for a universal standard.
Buying and substitution checklist
The most direct parts to look for are a Nokia 5110/3310 PCD8544 LCD module and a Raspberry Pi Pico. A breadboard and jumper wires are useful optional prototyping supplies. When comparing listings, confirm that the board actually identifies the PCD8544 family, shows the same functional labels, and states its supply and logic requirements. A product title alone is not enough.
If you select a different breakout, adapt the table rather than forcing its pins into the example order. If you select a bare handset LCD, treat it as a separate reverse-engineering project. An electronics supplier such as Adafruit publishes a relevant display guide, but its computer-oriented pin assignments should not be mistaken for Pico GPIO numbers.
Frequently Asked Questions
Can I connect any Nokia 3310 LCD directly to the Pico 3V3 pin?
Only a documented breakout that specifies a compatible 3.3 V supply should use the example 3V3 connection. A bare handset LCD reference lists a 2.8 V supply and may require different regulation or interface circuitry.
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Are GP18 and GP19 physical pin numbers?
No. They are GPIO identifiers. Use the official pinout for your particular Pico board to locate those GPIOs on the physical header.
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What if my module calls DIN MOSI or CE SCE?
Use the functional equivalent: DIN is serial data, CLK is serial clock, CE or SCE is chip select, and D/C is the command/data control line.
Why is the screen blank even though the backlight is on?
Check VCC and GND, the PCD8544 driver selection, SPI0 pins, CE/CS, D/C, reset, and contrast. A lit backlight does not prove that the controller is receiving valid commands.
Can I use a Nokia 7210 or another phone schematic for the 3310 keypad?
No. Another handset schematic can illustrate matrix scanning, but connector order and matrix labels vary by model. Map the exact 3310 keypad with its documentation or continuity testing.
How many Pico GPIOs does the original keypad need?
The exact count depends on the number of distinct row and column lines in your assembly. Determine that count from the traced matrix rather than assuming one GPIO per key.
Is a separate matrix keypad easier?
Usually yes, because its row and column labels and connector are documented. It is the simpler choice when preserving the original 3310 buttons is not required.
Should I add the keypad before testing the display?
No. Bring up the display alone, run a simple pattern, then trace and connect the keypad. This keeps display wiring faults separate from matrix-scanning faults.
The Bottom Line
For a documented PCD8544 breakout, start with VCC to 3V3, GND to GND, DIN to GP19, CLK to GP18, D/C to GP20, RST to GP21, CE/CS to GP17, and optional BL/LED to GP22. Treat those as example assignments, verify every label, and test the display before adding a keypad. A bare 3310 LCD and the original keypad require their own connector, voltage, and continuity checks.
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