FAQ
TL;DR: Expect 200–600+ hours for an HMI with analog I/O, touchscreen, and AC motor control; “it’s quite [a] project.” [Elektroda, Mark Harrington, post #21660135]
Why it matters: This FAQ helps PLC-to-embedded movers pick boards, plan effort, and avoid real-time and analog pitfalls for medical HMI builds.
Quick Facts
- Typical analog input on suggested boards: 0–3.3 V, 10‑bit (0–1023), with simple 4–20 mA conversion. [Elektroda, Robin Moss, post #21660134]
- .NET Micro Framework boards can add ~20 ms latency; FEZ offers realtime via RLP. [Elektroda, Robin Moss, post #21660127]
- Effort planning: prototype-to-product often spans 200–600+ developer hours. [Elektroda, Mark Harrington, post #21660135]
- Android/Linux path: Java app with XML UI; OS handles much device plumbing. [Elektroda, Ralph Pruitt, post #21660129]
- Starter HMI boards discussed: FEZ Cobra and Netduino Plus, both with active communities. [Elektroda, Robin Moss, post #21660127]
What’s a practical starter board for HMI with a touchscreen?
FEZ Cobra and Netduino Plus are entry-friendly and community-backed. They support touch UIs and peripherals. Note that .NET Micro Framework adds latency, so evaluate response time. FEZ’s RLP lets you offload time‑critical routines. Start with dev kits, then migrate to custom PCBs. [Elektroda, Robin Moss, post #21660127]
Can these boards read my analog sensors directly?
Yes, their ADCs accept 0–3.3 V with 10‑bit resolution (0–1023). For 4–20 mA loops, use a shunt and scale to 0–3.3 V. Serial sensors like RS‑485 inclinometers also connect with proper transceivers. “Serial data is no problem either.” Validate noise and grounding early. [Elektroda, Robin Moss, post #21660134]
How many hours should I budget to move from PLCs to embedded?
Plan for 200–600+ hours depending on features, safety, documentation, and validation. Networking, motor control, and HMI polish expand scope. One contributor estimated “600 Plus” for a robust solution. Timebox learning spikes and keep noncritical features for phase two. [Elektroda, Mark Harrington, post #21660135]
Should I choose Android or Embedded Linux for the HMI?
Android offers fast UI development in Java with declarative XML layouts. Many tasks are off‑the‑shelf, reducing OS plumbing. Boards like Freescale i.MX53 run Android for rich touch interfaces. Validate real‑time needs and use external controllers for tight loops. [Elektroda, Ralph Pruitt, post #21660126]
Is Android UI coding heavy for this use case?
UI scaffolding is quick since Android handles views and events, and XML defines layouts. “The app and underlying code is Java.” The main learning curve is Android’s component model. Prototype screens first, then integrate hardware services. [Elektroda, Ralph Pruitt, post #21660129]
Do I need a real-time OS for motor control?
If your control loop needs sub‑millisecond timing, avoid pure .NET MF loops. Expect ~20 ms framework overhead. Offload timing‑critical PWM or FOC to native code or a dedicated MCU while the HMI runs managed code. [Elektroda, Robin Moss, post #21660127]
What about the load cells—can I skip the expensive conditioner?
Your current design uses a signal conditioner and a Phoenix analog module. Maintain equivalent conditioning or replace with a suitable front‑end before the MCU’s ADC. Budget time to validate accuracy and drift across temperature. [Elektroda, Peter Halick, post #21660132]
How do I connect an RS‑485 inclinometer to an HMI board?
Use an RS‑485 transceiver and match baud, polarity, and termination. Cobra‑class boards can handle serial framing in software. Keep cable shielding and biasing correct to avoid intermittent data dropouts. [Elektroda, Robin Moss, post #21660134]
Which microcontroller families are safest bets for community help?
Pick mainstream lines like AVR or PIC to tap large communities and examples. This reduces bring‑up risk and accelerates debugging. Decide based on available libraries, tools, and your team’s skills. [Elektroda, Joe Wolin, post #21660124]
What skills or components inflate project time the most?
Networking stacks (Wi‑Fi/Bluetooth), secure comms, motor PWM control, and multi‑device integration add effort. Server links, RS‑232/Ethernet bridges, and radio modules like XBee expand scope. Expect research and validation cycles. [Elektroda, Mark Harrington, post #21660135]
What is the .NET Micro Framework, and when is it OK?
.NET MF lets you write embedded apps in C# on boards like FEZ and Netduino. It simplifies UI and logic but adds ~20 ms latency. Use it for HMI and supervisory tasks; push tight control to native layers. [Elektroda, Robin Moss, post #21660127]
I’m an Arduino‑savvy mechanical engineer—can I self‑deliver?
Yes, with scope control. Boards discussed expose analog inputs and serial easily, easing transition from PLCs. Aim for a working HMI first, then add motor control. Timebox to 200 hours for MVP, expand afterward. [Elektroda, Robin Moss, post #21660134]
How do I quickly prototype an Android‑based HMI?
- Choose an i.MX53‑class board that runs Android.
- Build the UI in XML and app logic in Java.
- Bridge hardware via serial, USB, or Ethernet and test end‑to‑end.
“Android takes care of much of the work of the OS.” [Elektroda, Ralph Pruitt, post #21660126]
What’s a reasonable definition of “incredibly easy to develop” here?
In this context, it means rapid HMI iteration, built‑in analog and serial I/O, and active forums for answers. FEZ and Netduino fit this, with the caveat of real‑time latency. RLP provides a path for time‑critical routines. [Elektroda, Robin Moss, post #21660127]
Any edge cases I should plan for before committing?
Plan for failure modes: serial framing errors, ADC saturation beyond 3.3 V, and motor stalls during latency spikes. Add hardware protection and watchdogs. Validate the 20 ms managed overhead against your control loop budget. [Elektroda, Robin Moss, post #21660127]
How can I find the right embedded talent if I don’t DIY?
Target developers experienced with AVR or PIC, as suggested, and review community contributions. Share a lean spec and ask for a fixed‑scope prototype quote. Prioritize candidates with HMI and motor‑control portfolios. [Elektroda, Joe Wolin, post #21660124]
