555 Calc vs PLC
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
555 Calc
This utility app helps engineers and hobbyists calculate resistor values for circuits using the Timer IC 555. Simply input frequency, duty ratio, and capacitor values to get the required resistor outputs.
- Calculate resistor values
- Input frequency
- Input duty ratio
- Input capacitor value
- Timer IC 555 circuit design
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This App calculates registors value, when designing the circuit using Timer IC 555. How to (1) Input Frequency value. (2) Input Duty Ratio. (3) Input C1 Value. (4) Touch ‘Calculate’ button. (5) Registors value will be displayed. Note. * Set Duty Ratio to 50 ~ 99. * If you set Duty Ratio to 50, R1 value will be set to 0.
PLC
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PLC-Inspector is a professional diagnostic tool for Siemens LOGO! controllers. Read memory, follow changes live and set registers, over Modbus/TCP, directly from iPhone, iPad or Mac. KEY FEATURES • Memory reading VM memory, analog inputs (AI) and analog outputs (AQ) of your LOGO! in real time. • Register writing Enter values in decimal or hexadecimal and send them to the controller. The app checks what the controller reports back and says so separately when the confirmation does not match the request. • Safeguarded writing Write mode has to be switched on deliberately and expires when you leave the view. Before every write there is a confirmation showing register and value in plain text, which can be switched off for a working session. • Bit-level visualisation Every register as a 16-bit value with colour-coded bit display. • Change detection Changed values are highlighted in orange. Jump between changes with the arrow buttons. • Auto-refresh Automatic updates in intervals from 0.5 to 10 seconds. • Multiple stations Manage any number of PLC stations with individual settings. APPLICATIONS - Commissioning and fault finding on site - Mobile process monitoring - Analysis of memory contents - Training and education TECHNICAL DETAILS - Protocol: Modbus/TCP (default port 502) - Reading: Read Holding Registers (FC 03), automatic splitting above 125 registers - Writing: Write Single Register (FC 06) with echo verification - Supported controller: Siemens LOGO! 8 (0BA8) NOTE The app needs a network connection to the LOGO! controller. The Modbus server must be enabled in LOGO!Soft Comfort. Developed by spiritdev Softwareentwicklung GmbH - your partner for industrial software solutions.
Screenshots
Verdict
The clearest difference is ads: PLC at none against 555 Calc's shown. PLC also leads on update cadence (every 2 weeks vs every 20 months). 555 Calc's advantage is iOS requirement (11.0 vs 17.0). On price, in-app purchases and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Neither carries in-app purchases, so what you see is what you pay.
555 Calc ships an update every 20 months, PLC every 2 weeks. The most recent releases landed on September 27, 2026 and October 6, 2026 respectively.
| Parameter | 555 Calc | PLC |
|---|---|---|
| Price | Free | Free |
| Rating | 4.0 (3 ratings) — better | — |
| Positive reviews | 50.0% of reviews | — |
| Number of ratings | 3 — better | — |
| Update frequency | Every 20 months | Every 2 weeks — better |
| Ads | Yes | No — better |
| In-app purchases | No | No |
| Monetization | Ad-supported | — |
| Devices | iPhone, iPad, iPod | iPhone, iPad, Mac |
| Requires iOS | 11.0 — better | 17.0 |
| Further details — not scored | ||
| Size | 18 MB | 4 MB |
| Age rating | 4+ | 4+ |
| Developer | Jibiki Works | spiritdev Softwareentwicklung GmbH |
In-app purchases
555 Calc
No in-app purchases
PLC
No in-app purchases









