Siemens LOGO! 8 Two-Button Dimmer with Short/Long Press Logic

1. Overview

The Siemens LOGO! 8 logic module is a compact micro-PLC frequently used for small building-services, machine-control, and lighting-control tasks. One of the most common lighting applications is a 0–10 V dimmer controlled by two momentary push-buttons (UP and DOWN). The required behaviour is:

• Short press of UP (< 0.5 s) → output jumps to full brightness (level 100).
• Long press of UP (> 0.5 s) → output ramps up slowly.
• Short press of DOWN (< 0.5 s) → output jumps to OFF (level 0).
• Long press of DOWN (> 0.5 s) → output ramps down slowly.

This article resolves the typical open question when programming this application: where exactly must the "set-light-to-100" output (B008) be connected, and how is the same behaviour obtained with a cleaner analog-counter block in LOGO!Soft Comfort V8.3? The solution is built around the LOGO! 8.3 base module plus the LOGO! AM2 AQ analog-output expansion (part number 6ED1055-1MM00-0BA2), which provides the actual 0–10 V signal to the LED-driver or 1–10 V ballast.

2. Hardware Bill of Materials and Terminal Wiring

The base LOGO! 8.3 module does not contain an analog output, so an AM2 AQ module is mandatory for any 0–10 V dimming task.

Wire the two push-buttons between the LOGO! +24 V terminal and the digital inputs I1 (UP) and I2 (DOWN). The AM2 AQ is snapped to the right of the base module and the analog output terminal AQ1+ / AQ1- is wired to the dim input of the driver. Shield the analog cable if the run exceeds 2 m, and observe the polarity printed on the AM2 AQ front panel (Pin 1 = +, Pin 2 = -).

3. LOGO! 8 Firmware and LOGO!Soft Comfort Version Compatibility

The same program does not transfer cleanly between every LOGO! generation. The version-aware behaviour that matters for the dimmer is summarised below.

Reference: LOGO! 8.3 System Manual and LOGO!Soft Comfort V8.3 Online Help.

4. Function Block Program Architecture

The full program uses eight to eleven standard LOGO! blocks. The block-numbering convention below matches the user's original file and is preserved here for reference.

The 0.5 s threshold is the determining constant of the algorithm. If the threshold is altered, both TH values in B001 and B002 must be updated together.

5. Implementing the Short/Long Press Detection

The 0.5 s threshold is realised with two parallel branches, one per push-button.

1. Wire I1 (UP) to the input of B002 (on-delay, TH = 0.5 s).
2. Wire I2 (DOWN) to the input of B001 (on-delay, TH = 0.5 s).
3. Add a positive edge trigger on the Set (S) input of B008 directly from I1, so that every short release of UP raises a one-cycle pulse.
4. Add a positive edge trigger on the Reset (R) input of B007 from I2, mirroring the OFF action.
5. Wire the output of B002 to the Count-up enable input of the counter; wire B001 to the Count-down enable input.
6. Use the output of the pulse generator (B004) as the count clock for B011, so that the level advances only while a long-press flag is true.

Press-time behaviour mathematically:

• If t_press < 0.5 s, B001/B002 stay 0. Edge detectors on I1/I2 generate one pulse on B008 (Set) or B007 (Reset).
• If t_press > 0.5 s, B001/B002 latch at 1. The clock from B004 then counts B011 up or down.
• If t_press = 0.5 s, the On-delay transition fires exactly once on release. Add a 50 ms hysteresis in B001/B002 to avoid simultaneous Set and Reset.

The number of steps traversed while ramping is computed as:

t_dim  =  (level_target - level_start) × pulse_period
        =  100 × 0.2 s
        =  20 s end-to-end (full off → full on)

Adjust the pulse period in B004 to taste. 0.1 s yields a 10-second ramp; 0.5 s yields 50 s.

6. Wiring the B008 "Set Light to 100" Output

The user's question is specifically: where does the output of B008 connect? The answer is the Set (S) input of B011, not the count input. On the Up/Down Counter (or the Analog Counter) block, the S input loads the parameter SV into CV irrespective of the current value, which is exactly what is required for "go to full brightness instantly".

1. In the LOGO!Soft Comfort editor, locate B011.
2. Identify the connector labelled S on the block symbol (top-left input pin).
3. Click the connector, drag a wire to the output pin Q of B008.
4. Compile the program (Tools → Compile → PC → LOGO!) and verify that B008 is now listed as connected in the program information window.

Behaviour after connection:

7. Alternative Implementation: Analog Counter Block

For new programs in LOGO!Soft Comfort V8.3, the cleaner solution is to use the dedicated Analog Counter block (B030–B039 typically) instead of the discrete-edge architecture. The Analog Counter block already provides dedicated Set and Reset inputs and exposes the current value as an analog signal that can be wired directly to AQ.

This block eliminates the B008 "where do I connect it" problem because the Set/Reset inputs are visible on the block symbol by default. It also removes the need for AMx multiplexers, which is the source of the LOGO! 8.3 load error discussed in Section 3.

8. 0–10 V Analog Output Scaling

The AM2 AQ module provides two 0–10 V outputs with 10-bit resolution (1024 steps, 1 step ≈ 9.77 mV). LOGO!Soft Comfort exposes the analog value as an integer 0–1000 in the AQ parameter; the hardware scaling is fixed by Siemens.

The B011 value range (0–100) is wired to AQ1 either directly through a scaling Analog Amplifier (gain = 10) or implicitly when B011 is replaced by the Analog Counter described in Section 7. The voltage equation is:

V_AQ1 (V)  =  (AQ_value / 1000) × 10 V
            =  (B011_value / 100) × 10 V
            =  B011_value × 0.1 V

Useful intermediate points:

Many commercial LED drivers clamp their input below 1 V to off and above 9 V to full on, so B011 = 1 (≈ 0.1 V) may already produce no light. If the lamp never goes fully off, insert an Analog Threshold Switch with ON = 1 and OFF = 0 between B011 and AQ1 to force a binary off state below 1.

9. Commissioning Procedure and Verification

Follow this sequence on first power-up. Each step has a binary pass/fail criterion that can be observed on the LOGO! display or in LOGO!Soft Comfort Online → Observation.

1. Connect the LOGO! 8.3 base to the PC via Ethernet, set the IP, and click Tools → Transfer → PC → LOGO!. The transfer log must show OK and no AMx warnings.
2. Switch LOGO! to RUN. The status line on the display should read RUN, not STOP or ERROR.
3. Short-press I1 (UP). Verify on AQ1 that the voltage jumps to 9.8–10.0 V within one scan cycle. If not, B008 is not wired to B011 S (see Section 6).
4. Short-press I2 (DOWN). Verify AQ1 = 0.0 V within one scan cycle.
5. Long-press I1 for 3 s. AQ1 should rise smoothly from 0 to ≈ 1.5 V (15 steps × 0.1 V). At 0.2 s / step, 3 s ≈ 15 steps.
6. Long-press I2 for 5 s. AQ1 should fall proportionally. Stop short of zero and verify that the counter holds (no drift over 60 s).
7. Power-cycle the LOGO! and verify whether the dim level is retained. To retain, mark B011 as Remanent in the block properties.
8. Force a max-brightness event by sending a Set pulse from LOGO!Soft Comfort Online → Simulation to B008. Confirm CV = 100 in the observation panel.

Verification formula for ramp tests:

Expected AQ (V)  =  (t_press - 0.5 s) / pulse_period × 0.1 V
                 =  (3.0 - 0.5) / 0.2 × 0.1
                 =  1.25 V (within ±0.1 V tolerance)

10. Troubleshooting Matrix

Additional diagnostics are available in LOGO! 8 System Manual (entry ID 109741041), specifically chapters 4.4 (function blocks) and 7 (analog value processing).

11. Frequently Asked Questions