The [LF Audio](https://lf-audio.com) HPVM and HPVM Pro are high-precision Bluetooth-enabled voltage meters designed for automotive and car audio applications. Both units connect to the free [LF Audio AuralSync™ app](https://lf-audio.com/pages/support) and offer real-time voltage monitoring with highly customizable displays. This article provides a complete overview of both models, their features, and guidance on which model best suits your needs.

The HPVM (High Precision Voltage Meter) is a compact, precision-engineered voltmeter built for automotive environments. It monitors your vehicle's electrical system in real time, displaying voltage data on a full-color LCD screen with a variety of customizable gauge faces.

Key capabilities include:

| Feature | HPVM | HPVM Pro |

| **Voltage Monitoring Channels** | 2 | 4 |

| **Display Size** | 2.0" TFT HD IPS LCD | 2.0" TFT HD IPS LCD (larger physical unit) |

| **Display Resolution** | 240×320 pixels / 65k color | 240×320 pixels / 65k color |

| **Visual Refresh Rate** | 33 FPS | 33 FPS |

| **Voltage Measurement Range** | 1v–18v | 1v–18v |

| **Supply Voltage** | 3v–18v | 3v–18v |

| **Accuracy** | 99.99% (+/- 0.002v) | 99.99% (+/- 0.002v) |

| **Precision** | 1mV — 3 decimal places (e.g. 15.234v) | 1mV — 3 decimal places (e.g. 15.234v) |

| **Sample Rate** | 330 samples/sec per channel | 330 samples/sec per channel |

| **Bluetooth / App Support** | Yes — AuralSync™ | Yes — AuralSync™ |

| **OTA Firmware Updates** | Yes | Yes |

| **Deep Sleep Mode** | Yes | Yes |

| **Size** | 71mm × 61mm × 25mm | Physically larger |

| **Weight** | 3.0 oz | — |

| **Gauge Faces** | 10 | 10 |

Both the HPVM and HPVM Pro sample at **330 samples per second per channel**, providing near-instantaneous voltage readings accurate to **1 millivolt** (three decimal places). This level of precision allows you to detect even subtle changes in your vehicle's electrical system.

Both units connect wirelessly to the free **[LF Audio AuralSync™ app](https://lf-audio.com/pages/support)**, available for:

The app allows you to configure gauge faces, set custom voltage ranges, assign colors, calibrate channels, and push firmware updates — all wirelessly.

The optional **[AuralSync Companion Smartwatch](https://lf-audio.com/products/auralsync-companion-smartwatch)** is also compatible with both units for wrist-based monitoring.

Choose from **10 gauge face designs** and customize:

The HPVM's Deep Sleep mode draws only **167 milliwatts** when it detects a gradual voltage drop without transients. This is engineered to protect your battery, taking up to **294 days** to deplete a fully charged 100Ah 12V AGM battery.

While in Deep Sleep, the unit continues collecting voltage samples and will alert you with a **red warning signal** when it wakes, reporting:

See [Power Management](Power_Management.md) for full details.

The HPVM is housed in a **solid aluminum case** with:

Firmware can be updated wirelessly via **Bluetooth** through the AuralSync™ app, or via **Wi-Fi** (depending on firmware version). Future firmware versions will also support uploading data directly to a **web dashboard** viewable on desktop or mobile.

| Use Case | Recommended Model |

| Monitoring a single battery or power source | HPVM |

| Monitoring two voltage points (e.g., main battery + secondary) | HPVM |

| Monitoring four independent voltage sources simultaneously | HPVM Pro |

| Complex car audio builds with multiple amplifier banks | HPVM Pro |

| Builds where physical space is limited | HPVM |

The HPVM Pro holds the following certifications:

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This guide walks you through the physical installation and wiring of your [LF Audio](https://lf-audio.com) HPVM or HPVM Pro High Precision Voltmeter. Connecting your unit is straightforward and requires only basic wiring knowledge. Follow the steps below to get your voltmeter powered up and measuring correctly.

The HPVM has a connector with the following pin positions:

| Pin Position | Label | Function |

| **Leftmost Pin** | 12V Power | Constant 12V power from your battery |

| **Second Pin** | Remote | Remote turn-on signal from your head unit |

| **Rightmost Pin** | Ground | Chassis ground connection |

| **Third Pin** *(optional)* | Secondary Channel | Secondary voltage measurement input |

Connect the **leftmost pin** to a **12-volt battery source**, such as your vehicle's main battery or a fused power distribution block.

Connect the **second pin** to a **remote audio turn-on signal source**, such as the remote output line from your head unit (car radio).

This allows the HPVM to power on and off with your audio system.

Connect the **rightmost pin** to a solid **chassis ground** point.

Optionally, connect the **third pin** to a secondary voltage source you wish to monitor independently.

**Important notes about the secondary channel:**

| Configuration | What the Unit Measures |

| Primary channel only | Voltage between the 12V pin and Ground pin |

| Secondary channel connected | Independent voltage on the secondary input |

The HPVM features **wiring terminals on both the back and bottom** of the unit, giving you flexibility in how you route your wiring and mount the device in your vehicle. This also contributes to a clean, professional installation appearance.

If you are running long wires from your battery or power source to the voltmeter (e.g., from the trunk of a vehicle to the dashboard), the resistance in the wire can cause a slight voltage drop that affects measurement accuracy.

The [LF Audio AuralSync™ app](https://lf-audio.com/pages/support) allows you to **calibrate each voltage sensing channel** to compensate for this impedance or resistance. See the [Calibration Guide](Calibration_Guide.md) for full instructions.

Once your unit is physically wired and powered on:

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This guide walks you through pairing your [LF Audio](https://lf-audio.com) HPVM or HPVM Pro High Precision Voltmeter with your smartphone for the first time using the [LF Audio AuralSync™ app](https://lf-audio.com/pages/support). Pairing establishes an encrypted Bluetooth connection between your phone and the voltmeter, enabling real-time data streaming and full configuration access.

Make sure you have the following ready:

The AuralSync™ app is available on:

Your HPVM has a unique Bluetooth PIN code assigned to it at the factory. You will need this PIN during the pairing process.

Flip your HPVM unit over. You will find a **sticker on the back** with your unit's unique PIN code.

Starting with **firmware version 1.4**, the HPVM displays diagnostic information including the Bluetooth PIN code on boot:

If you missed the PIN on boot and need to see it again:

Launch the [LF Audio AuralSync™ app](https://lf-audio.com/pages/support) on your iOS or Android device.

Tap the **"+" (plus) button** in the **bottom right corner** of the app's main screen.

The app will scan for nearby devices. You will see your unit listed. The **default device name** is:

Tap on your unit in the list.

You will be prompted to enter your unit's unique PIN number.

Enter the PIN found on the sticker on the back of your unit (or displayed on the unit's screen during boot).

After entering the PIN, tap **"Pair"** to confirm.

The app will establish an **encrypted Bluetooth connection** and pair with your device.

Navigate to the **main menu** of the AuralSync™ app. You should see:

| Status | What It Means |

| Streaming data / Paired | Successfully connected — live voltage data is being received |

| Device not found | Unit may be off, out of range, or Bluetooth not enabled |

| Pairing failed | Incorrect PIN entered, or location services disabled (Android) |

| Issue | Solution |

| Unit not appearing in the app | Ensure the HPVM is powered on and Bluetooth is enabled on your phone |

| PIN prompt not appearing on Android | Slide down the notification panel to find the Bluetooth pairing request |

| Pairing fails on Samsung device | Enable Location Services in your phone's settings and try again |

| Forgot PIN / can't find sticker | Reboot the unit twice (as described above) to display PIN on screen |

| Connection drops frequently | Ensure the unit and phone are within Bluetooth range; check for interference |

For additional help, see the [Troubleshooting Guide](Troubleshooting.md).

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The [LF Audio AuralSync™ app](https://lf-audio.com/pages/support) gives you full control over how your HPVM or HPVM Pro displays voltage data. This article covers all available display customization options, channel configuration, and general settings accessible through the app. Before proceeding, ensure your unit is paired and connected — see the [Bluetooth Pairing Guide](Bluetooth_Pairing.md).

The configuration panel is organized into **tabs**. Key settings are distributed across these tabs as described below.

The HPVM supports **10 different gauge face designs**, each with its own set of customizable options.

You can assign custom colors to each voltage range zone on your gauge. For example:

**Example:** Change the "good voltage" indicator from green to purple — simply select the zone and pick your new color. The change applies immediately.

You can define custom voltage ranges to match your specific battery chemistry or system setup. This is especially useful if you run:

The app allows you to choose which voltage channels are visible on your gauge:

Navigate to the channel selection area in the app and toggle which channels you want displayed.

You can configure the **secondary channel to display as the primary reading** on your gauge face. This is useful when the secondary voltage source is what you want to monitor most prominently.

**How to do this:**

Once enabled, the secondary channel's voltage will appear as the main reading on your gauge face.

Enable **Voltage Min/Max Hold** to have your gauge faces track and display the minimum and maximum voltages recorded during the entire session.

When enabled, the gauge faces will continuously display both the session minimum and maximum voltages alongside the live reading.

You can assign a **custom name** to your HPVM unit. This is helpful when running multiple units simultaneously (e.g., in a multi-amplifier build).

The custom name will appear in the app's main menu, making it easy to identify each unit at a glance.

From within the device view in the app, you can:

See the [Firmware Updates Guide](Firmware_Updates.md) for full details on updating your unit.

| Setting | Where to Find It | Notes |

| Gauge face selection | Configuration → Display | 10 faces available |

| Color customization | Configuration → Display | Per voltage zone |

| Voltage ranges (min/max) | Configuration → Display | Per channel |

| Sub-ranges | Configuration → Display | For color zone thresholds |

| Channel selection | Configuration → Channels | HPVM: 2ch / Pro: 4ch |

| Secondary as primary | Configuration → Channels | Toggle on/off |

| Min/Max hold | Configuration → Third tab | Per session |

| Device name | Configuration → Third tab | Custom label |

| Deep Sleep settings | Configuration → Third tab | See Power Management guide |

| Calibration | Configuration → Third tab | See Calibration guide |

| Firmware info & updates | Device view → Update banner | See Firmware guide |

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This guide explains how to calibrate the voltage sensing channels on your [LF Audio](https://lf-audio.com) HPVM or HPVM Pro High Precision Voltmeter. Calibration allows you to correct for voltage drift in the unit itself, as well as compensate for resistance introduced by long wire runs between your battery and the voltmeter. Before calibrating, ensure your unit is wired and paired with the [AuralSync™ app](https://lf-audio.com/pages/support) — see the [Installation Guide](Installation_Guide.md) and [Bluetooth Pairing Guide](Bluetooth_Pairing.md).

Even highly accurate instruments can experience minor **voltage drift** over time or due to manufacturing tolerances. Additionally, if you are running long wires from your power source to the voltmeter, the **resistance and impedance** of those wires can cause a measurable voltage drop, resulting in readings that are slightly lower than the actual voltage at the source.

Calibration allows you to apply a **multiplier correction** to the voltage divider inside the unit, bringing its readings into alignment with a known-accurate reference meter.

**Common reasons to calibrate:**

Connect your digital multimeter **directly to the same measurement points** as your HPVM (i.e., to the same pins or at the same location in the circuit). This gives you a trusted reference voltage reading to compare against.

The third tab contains the calibration (voltage drift correction) settings for each channel.

Observe the voltage displayed by:

**Example:** If your multimeter reads **11.8V** and your HPVM also reads **11.8V**, no calibration is needed. If there is a discrepancy, proceed to Step 4.

In the third tab, you will see a **variable adjustment field** for voltage drift correction. Use the **"+" and "–" buttons** to adjust the multiplier up or down.

Once the HPVM reading matches your reference multimeter, your calibration is complete. The setting is saved to the unit.

If you have a secondary voltage source connected to the **third pin** (secondary measurement channel), you can independently calibrate that channel as well.

If you are running wires from the back of your vehicle (e.g., trunk-mounted battery) to a voltmeter mounted near the front, the resistance in those wires will cause the voltmeter to read slightly lower than the actual battery voltage.

**To compensate:**

This process eliminates the error introduced by wire resistance and gives you accurate battery voltage readings regardless of wire length.

| Best Practice | Why It Matters |

| Use a quality reference multimeter (e.g., Fluke) | Cheap meters can introduce their own inaccuracies |

| Calibrate with the system at a stable, known voltage | Avoids calibrating against a fluctuating reading |

| Calibrate after any significant wiring changes | Wire runs affect resistance and therefore accuracy |

| Calibrate both channels independently | Each channel may have different drift characteristics |

| Re-check calibration after firmware updates | Updates may reset or affect calibration values |

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The [LF Audio](https://lf-audio.com) HPVM and HPVM Pro feature an advanced **Deep Sleep power management system** designed to protect your vehicle's battery when the car is off. This guide explains how Deep Sleep mode works, how to configure it, and how to interpret the data it collects while your vehicle is parked. Before configuring power management, ensure your unit is paired with the [AuralSync™ app](https://lf-audio.com/pages/support) — see the [Bluetooth Pairing Guide](Bluetooth_Pairing.md).

When a car is parked and the audio system is off, a poorly designed voltage monitor can itself become a **parasitic drain** on the battery. The HPVM's Deep Sleep mode is engineered to minimize this risk while still providing valuable battery health data.

Additionally, Deep Sleep mode enables the HPVM to act as a **battery health sentinel** — detecting excessive parasitic loads or a failing battery while the vehicle sits idle, and alerting you when you return.

The HPVM monitors the voltage on its power input continuously. When it detects a **gradual, sustained voltage drop** (consistent with a vehicle being turned off and the battery slowly settling), the unit enters Deep Sleep mode.

**Key trigger condition:** The voltage drop must be gradual and without transients (sudden spikes). This prevents the unit from entering sleep mode during normal audio system use, where voltage fluctuations are common.

| Mode | Power Draw |

| Normal operation | Full operation |

| Deep Sleep | **167 milliwatts** |

At 167mW draw, the HPVM can run in Deep Sleep for up to **294 days** on a fully charged 100 amp-hour 12V AGM battery before depleting it — making parasitic drain from the unit itself essentially negligible.

While in Deep Sleep mode, the HPVM:

The HPVM's **rapid response circuitry** detects a voltage spike (e.g., when the vehicle is started or the power supply voltage rises) and immediately reactivates the unit, resuming full operation.

When the HPVM wakes from Deep Sleep, it displays a **summary of what occurred during the sleep session**. If the voltage dropped below a critical threshold, you will see a prominent **red "Danger — Low Voltage" warning**.

The wake report includes:

| Data Point | Description |

| **Starting Voltage** | Voltage when the unit entered Deep Sleep |

| **Ending Voltage** | Voltage when the unit woke up |

| **Voltage Drop** | Total drop that occurred during the session |

| **Session Duration** | How long the unit was in Deep Sleep |

**Example:** If the unit slept for 30 seconds (simulated) and the voltage dropped significantly, it will wake and display "Danger — Low Voltage" along with the starting voltage, ending voltage, and total drop.

This data helps you identify:

Locate the **Deep Sleep** option and toggle it **on**.

Configure the **expected resting voltage** for your battery. This is the voltage you expect your battery to settle at when the vehicle is fully off and the battery is at rest.

The HPVM uses this threshold to determine when the voltage has dropped to an abnormal level and triggers the danger alert accordingly.

While in the third tab, you can also enable **Voltage Min/Max Hold**. When enabled, the gauge faces will display the minimum and maximum voltages recorded across the entire session — useful for understanding the full range your system experienced.

| Scenario | HPVM Behavior |

| Car turned off, voltage gradually drops | Enters Deep Sleep mode |

| Voltage spike detected (car started) | Wakes immediately, resumes full operation |

| Voltage drops significantly during sleep | Stores the event; displays red warning on wake |

| Normal voltage during sleep | Wakes normally, no warning displayed |

The Deep Sleep system effectively turns your HPVM into a **passive battery health monitor** whenever your vehicle is parked. Over time, you can use the wake reports to track trends:

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Keeping your [LF Audio](https://lf-audio.com) HPVM or HPVM Pro firmware up to date ensures you have access to the latest features, performance improvements, and bug fixes. This guide explains how to check for firmware updates and install them using the [LF Audio AuralSync™ app](https://lf-audio.com/pages/support). Firmware updates can be delivered via **Bluetooth** or **Wi-Fi**, depending on your current firmware version.

| Method | Requirements | Notes |

| **Bluetooth (via AuralSync™ app)** | Smartphone/tablet + AuralSync™ app | Available on all firmware versions |

| **Wi-Fi** | Wi-Fi network + supported firmware version | Available on select firmware versions |

The **orange header** is your visual indicator that a firmware update is available. It will display:

Tap the **orange header** in the device view of the app. A pop-up will appear with:

Tap **"Install"** to begin the firmware transfer.

During the transfer, you will see progress indicators on **both** your phone and the HPVM unit itself:

Once the firmware transfer is complete, the HPVM will **automatically restart**. No action is required on your part.

After restarting, the unit will resume normal operation with the new firmware installed.

*(Available on select firmware versions)*

When you tap the orange update header, the app displays the **release notes** for the new firmware version, including:

Always review these notes before installing to understand what will change on your unit.

| Issue | Possible Cause | Solution |

| No orange header visible | Firmware is already up to date | No action needed |

| Update not starting | Bluetooth connection dropped | Ensure phone is close to unit; reconnect and try again |

| Update appears to stall | Temporary Bluetooth interference | Stay within range; avoid other Bluetooth devices nearby |

| Unit not restarting after update | Update may still be processing | Wait 60 seconds; if no restart, power cycle the unit manually |

| App shows error during update | Low phone battery or app crash | Ensure phone is charged; reopen app and attempt update again |

For persistent update issues, see the [Troubleshooting Guide](Troubleshooting.md).

| Version | Notable Features |

| **1.4** | Diagnostic info + Bluetooth PIN displayed on boot screen |

| **2.0.1** | Available via Bluetooth update (see feature notes in app) |

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This guide covers the most common issues users encounter with the [LF Audio](https://lf-audio.com) HPVM and HPVM Pro High Precision Voltmeters, along with step-by-step solutions. If you cannot resolve your issue using this guide, refer to the relevant detailed article linked in each section or contact LF Audio support.

Before diving into specific issues, run through this checklist:

| Possible Cause | Solution |

| Unit is not powered on | Check wiring connections — ensure 12V and ground are properly connected (see [Installation Guide](Installation_Guide.md)) |

| Bluetooth is disabled on phone | Enable Bluetooth in your phone's settings |

| Phone is out of range | Move your phone closer to the HPVM unit |

| App needs refresh | Close and reopen the AuralSync™ app and tap the "+" button again |

On Android devices, the Bluetooth pairing PIN prompt may appear in the **notification panel** rather than as a pop-up dialog.

**Solution:**

**Symptom:** Pairing attempt fails or the device is not discovered.

**Solution:**

| Possible Cause | Solution |

| Phone too far from unit | Keep phone within typical Bluetooth range (~10 meters / 30 feet) |

| Bluetooth interference | Move away from other Bluetooth devices or Wi-Fi routers operating on 2.4GHz |

| App running in background | Keep the AuralSync™ app open in the foreground during use |

The PIN is available in two places:

See the [Bluetooth Pairing Guide](Bluetooth_Pairing.md) for full details.

| Possible Cause | Solution |

| No 12V power connected | Verify the leftmost pin is connected to a 12V source |

| No ground connection | Verify the rightmost pin is connected to a solid chassis ground |

| Blown fuse | Check for an inline fuse on the power wire and replace if blown |

| Voltage too low | The HPVM requires a minimum of 3V to operate |

| Possible Cause | Solution |

| Ground connection is poor | Re-check and clean the ground connection point |

| Measuring secondary channel only | Verify which channel is configured as primary in the app |

| Calibration offset is extreme | Reset the calibration multiplier in the app (third tab) |

**Symptom:** The HPVM reading doesn't match a trusted external multimeter.

**Solutions:**

| Possible Cause | Solution |

| Unit is in Deep Sleep mode | Start the vehicle or increase voltage above the sleep threshold to wake the unit |

| Unit is not powered | Check wiring connections |

| Display brightness | Check display settings in the AuralSync™ app |

**Solution:**

**Solution:**

**This is not an error.** If no orange header appears in the device view, your firmware is already up to date.