Single Push Button Toggle Circuit with Omron G2R-1-SN Relays

1. Problem Definition and Design Constraints

A single-pole, single-throw (SPST) momentary push button cannot toggle a load by itself; it has no memory. External memory is required, and the simplest external memory is an electromechanical relay with a self-holding (latching) contact. The objective in this reference is to design a single-push-button on/off toggle that drives a mains-voltage lamp load using four Omron G2R-1-SN(S) relays with 230 VAC coils and an ELMARK EL2-BW07 industrial momentary actuator. The bulb is a representative 230 V resistive/inductive load (incandescent, halogen, or switched-mode LED driver input).

The fundamental engineering constraint is that the classic capacitor-charge / capacitor-discharge timing trick used in DC one-button toggle circuits does not transfer directly to AC. An AC coil relay's magnetic flux collapses fully every half-cycle (10 ms at 50 Hz), so the contact releases within 5-10 ms of coil current removal, much faster than any RC time constant can extend. With pure AC coils the timing windows available for the four-relay cascade in Method 2 are measured in tens of milliseconds, which is why Method 1 (introducing a small DC rail) is the most reliable. The four methods below solve the same problem in different ways, with progressively less external hardware and progressively more reliance on component tolerances.

2. Component Specifications

2.1 Omron G2R-1-SN(S) Relay

The G2R-1-SN is a single-pole 10 A general-purpose relay in the Omron G2R family. The model code decodes as follows:

• 1 = 1-pole (SPDT, Form C, one common / one NO / one NC)
• S = Standard compact housing, 12.6 mm wide
• N = Mechanical action indicator + LED indicator (visible through the socket)
• (S) = Flux-proof / sealed construction (suitable for wave soldering and clean environments)

Key electrical ratings from the official datasheet (Omron Cat. No. J03S-E-01, document G2R_DS_E_5_1):

Source: Omron G2R Series Datasheet (J03S-E-01). Datasheet ordering URL on Omron Industrial Automation portal: G2R family product page.

The 230 VAC coil version you are holding is the G2R-1-SN(S) AC230. To build a clean DC toggle, swap it for the same-form-factor G2R-1-SN(S) DC12 or DC24. The base, contact rating, and pinout are identical; only the coil voltage differs. This is the key change that unlocks Method 1.

2.2 ELMARK EL2-BW07 Push Button

EL2-BW07 is a 22 mm panel-mount industrial push button in ELMARK's Economy-Line (EL2) range. The B in the code denotes a black bezel, W07 denotes a single-pole, momentary, flush-mount configuration. The contact block behind the operator is a single NO contact rated 6 A at 230 VAC (AC-12 / DC-12 utilization category). Mechanical life is 1,000,000 cycles minimum, electrical life 100,000 cycles at rated load. Operating force is roughly 2.5 to 4 N with 2.5 mm travel. The device is IP65 from the front when the supplied sealing gasket is fitted. The actuator has a single NO contact; for the two-relay methods below you need a second contact (a SPDT or DPDT contact block must be stacked behind the operator using EL2's modular holder). If your installation has the operator fixed and you cannot change the contact block, use Method 1 with the DC flip-flop — that is the method that requires only a single NO contact.

2.3 Load (Light Bulb) Sizing

Before selecting the final contact arrangement, calculate the worst-case inrush current. The bulb load is not purely resistive at turn-on:

Steady-state and inrush are both well inside the G2R's 10 A / 2,500 VA rating. If you size up to a 1,000 W halogen, the cold-filament inrush is 4.3 A × 10 = 43 A for ~200 ms; the G2R's electrical life derates for tungsten loads to about 1/3 of the resistive rating, so specify a 16 A relay (e.g., Omron G7L or G2R-1-SN-ASI variant) or use an SSR for high-inrush loads.

3. Why a Pure AC-Coil Single-Button Toggle is Non-Trivial

To make a one-button toggle, the push button must generate a brief pulse, and that pulse must change the state of a memory element. In a DC circuit the pulse is naturally produced by the charge/discharge of an RC network, the relay coil itself is part of that RC, and the relay's release time (5 ms for a DC G2R) is small compared to RC time constants of hundreds of milliseconds. A circuit such as V+ — 1kΩ — PB — [470 µF cap to V+] — [K1 coil to V-] with the K1 NO contact feeding back to hold the coil works reliably because the cap holds the coil above the must-release voltage for 100-200 ms after the button opens.

With a 230 VAC coil the same circuit does not work because:

1. AC polarity reversal. The coil sees a sinusoid that passes through zero 100 times per second. A polarized electrolytic cap cannot sit across an AC coil. Either use a non-polarized (motor-start) AC-rated film cap, or add a bridge rectifier so the cap sees DC.
2. High coil impedance. The 230 VAC coil resistance is ~22 kΩ. A cap that produces a useful time constant of 100 ms needs C = t / R = 0.1 / 22,400 = 4.5 µF at 400 V rating. This is physically possible (a 4.7 µF / 400 V X2 cap is small and cheap) but the energy stored (E = ½CV² = 0.10 J) is marginal to hold the relay's armature against its spring.
3. Zero-cross drop-out. A DC relay has a defined must-release voltage (10 % of rated). An AC relay's armature is held by flux that vanishes at every zero-cross, so the relay is really releasing 100 times per second and re-closing on the next peak. Adding capacitance only smooths the envelope, it does not give a clean DC release threshold.
4. Symmetry required. A one-button toggle needs the same pulse to set the latch and to break it. With AC, an RC network on the set side will release the latch in the same RC window, and the timing windows for "set" and "reset" cannot be made different by component choice alone. This is why Method 2 below cascades three timer relays — to create asymmetric timing windows.

4. Method 1 — DC Flip-Flop with G2R DC-Coil Relays

The most reliable method, and the one that uses all four of your G2R relays, is to add a small DC power supply and use the G2R family with DC coils. Replace your four AC230 G2R-1-SN(S) with G2R-1-SN(S) DC12 (or DC24, depending on your supply). Pinout and base are identical; only the coil label differs.

4.1 Power Supply

A 12 VDC / 500 mA wall-wart SMPS module is sufficient. Each G2R DC12 coil draws 43 mA at 12 V (530 mW). Four coils + the flip-flop IC + indicator LED = ~250 mA worst case, so a 500 mA supply has 100 % headroom. Add a 1 A fuse on the 230 VAC input of the SMPS and a 0.5 A polyfuse on the 12 V rail.

4.2 Toggle Circuit with CD4013

The CD4013 is a dual D-type flip-flop. We use one half as a toggle (T flip-flop made by tying Q̅ back to D). The Q output drives a G2R DC12 coil through a 1 kΩ base resistor + 2N2222 transistor (relay coil inrush is 4× the holding current for the first 5 ms; the 2N2222 saturates fully and absorbs the inrush). The G2R's NO contact then switches the 230 VAC load.

Schematic of the control board (low-voltage side, all 12 VDC):

Net list for the CD4013 section:

• U1 = CD4013BCM (SOIC-8 or DIP-14 with second half unused)
• R1 = 100 kΩ, R2 = 1 kΩ, R3 = 4.7 kΩ (base)
• C1 = 100 nF X7R (decoupling on VDD), C2 = 100 nF (debounce on CLK)
• C3 = 100 nF (power-on reset, R=100 kΩ)
• Q1 = 2N2222A or BC547
• D1 = 1N4148 (coil freewheel)
• K1 = G2R-1-SN(S) DC12 (drives the 230 VAC load)

4.3 Using the Other Three G2Rs

You have four relays. With Method 1 only K1 is needed to switch the load. The other three can be used productively:

• K2 — Status indicator. A second G2R DC12 wired to the Q̅ output through a separate 2N2222. K2's NO contact closes a 230 VAC indicator lamp (neon) in parallel with the load. This gives a "lamp is off" indicator on the panel — useful in stairwells and corridors.
• K3 — Master override. K3 wired in series with K1's NO contact (load side). A second push button (Keyswitch) energizes K3 to enable the toggle. Used as a "cleaning mode" lockout so the load cannot be energized while the enclosure is open.
• K4 — Interlock with a door contact or motion sensor. K4's NO contact in series with the 12 V rail feeding the whole toggle board. If a door contact opens, the toggle board loses power, the K1 coil de-energizes in 5 ms, and the load is forced OFF (fail-safe).

4.4 Power-Up State and Brown-Out Behavior

At power-up, the CD4013's Q output is undefined. Add a 100 nF cap from R (reset) to VDD and a 100 kΩ resistor from R to GND so that the flip-flop is held in reset for ~10 ms after VDD rises. This guarantees a defined OFF state. If the supply is bouncy (SMPS with no bulk cap), add a 47 µF electrolytic at the IC. The 2N2222 + 1 kΩ base resistor limits the base current to 12 mA, which is within the CD4013's 25 mA per-pin rating.

5. Method 2 — Two-Relay Response-Time Flip-Flop (AC Coils)

If you must keep the four 230 VAC coil G2R-1-SN(S) relays (e.g., the panel layout is fixed, the DC coil variants are not available), use this 2-relay flip-flop. The remaining two relays (K3, K4) drive the indicator lamp and an external alarm output as in Method 1.

5.1 The 1957 Allen-Bradley Topology

The original concept, dating to mid-century relay logic cabinets, is to use the relay's own operate time and release time to differentiate between a short press and a long press. A 2-relay version with one push button uses:

• K1: SPDT (Form C), 230 VAC coil, "load relay". K1's NO contact carries the lamp load.
• K2: SPDT (Form C), 230 VAC coil, "timing relay". K2's NC contact is wired in series with K1's coil latch path.
• PB: momentary NO push button (EL2-BW07 with single NO contact block).
• C1: 4.7 µF / 400 V X2 film capacitor across K2's coil, in series with R1 = 1 kΩ / 5 W resistor. The R-C across the AC coil extends the release time from 10 ms to roughly 200-300 ms.

5.2 Sequence of Operation

1. Initial (lamp off, K1 off, K2 off). Node A is de-energized. K1 NO is open, K2 NC is closed. K1 coil path is PB → K2 NC → K1 coil → N. K2 coil path is PB → R1+C1 → K2 coil → N (with K2 NC closed there's also a sneak path, but K1's open contact blocks it).
2. Button pressed. PB closes. Current flows through PB to node A. K1 coil energizes (K2 NC still closed, so K1 has a complete path). K1 NO closes after ~15 ms. K1 NO is in parallel with PB, so the latch holds after PB releases — except that K2's slow-release network is also charging through R1.
3. Button released quickly (< 50 ms). PB opens. K1 stays latched through K1 NO. K2 is still being charged by R1+C1; K2 has not yet pulled in. K2 NC remains closed. Lamp ON.
4. Button held longer (> 200 ms). C1 charges through R1 to the point where K2's coil voltage exceeds the must-operate threshold (80 % of 230 V). K2 energizes. K2 NC opens. The K1 latch path through K2 NC is broken. K1 de-energizes. Lamp OFF. (K2 releases after C1 discharges through R1, ~200-400 ms later.)
5. Button released after the long press. K2 releases after C1 discharges, K2 NC closes, K1's latch path is restored, and pressing PB again starts the cycle from step 2.

5.3 Choosing R1 and C1

The slow-release network is selected so that K2 pulls in at t = 200 ms after PB is held continuously. The C1 charge time constant is τ = R1 × C1 (the coil's 22 kΩ is in parallel and dominates — to a first approximation, ignore it). The coil's must-operate AC voltage is 0.8 × 230 = 184 Vrms. The cap voltage must reach 184 V across the coil. With the coil in parallel with C1, the divider is C1 || R_coil. Solve for the time to reach 184 V across that parallel combination when PB supplies 230 Vrms through R1.

Iterative design starting values that work in practice with the G2R-1-SN(S) 230 VAC coil:

• C1 = 4.7 µF ± 5 % 400 V X2 (MKP/X2 across mains class, e.g., EPCOS/TDK B3292* series)
• R1 = 1 kΩ ± 5 % 5 W wirewound (Yageo KNP series or similar)
• t_release_to_pickup ≈ 200-300 ms depending on the actual G2R coil tolerance (the 30 % must-release figure means 69 V is the dropout; 80 % must-operate means 184 V is the pull-in; the 184 V threshold is the design point).

5.4 Quirks of the AC-Coil Method

• Press-time-dependent. A short tap latches ON, a longer press resets to OFF. The 50-200 ms threshold is operator-dependent and is not reliable for production use. The original 1957 design used a heavy-duty industrial push button with a distinct detent, which masked this. The EL2-BW07 is a lighter actuator and the threshold will be more variable.
• Hum and buzz. The slow-release R-C across the AC coil produces magnetostrictive buzz in the relay frame. Mount the relay on rubber grommets if acoustic noise matters.
• Contact wear on K2 NC. K2's NC contact breaks the K1 coil current every time K2 picks up. The K1 coil's stored energy (~0.9 VA at turn-off) creates a 200 V inductive kick that arcs the NC contact. Add an RC snubber (100 Ω + 100 nF X2) across K2 NC.

6. Method 3 — Four-Relay Sequential Toggle (AC Coils)

Method 2 uses two relays. If you specifically need to use all four AC-coil G2R-1-SN(S) relays because the panel layout fixes four positions, the four-relay cascade is a direct extension. The principle is the same as Method 2 — a chain of slow-release timer relays — but the chain is longer, so the toggle window is wider and more predictable.

6.1 Topology

The chain is: PB → K1 → K2 → K3 → K4 → break K1 latch. K1 is the load relay. K2 and K3 are intermediate timer relays with progressively longer RC time constants. K4 is the release relay; its NC contact is in series with K1's latch path, and when K4 picks up, the latch breaks.

Required timing:

6.2 Two Push Button Contact Blocks

The cascade only fires when PB is held continuously. A quick tap closes and releases PB before K2 has time to pick up, so only K1 operates and latches. A long hold drives the chain to completion. The original 1957 design used a single push button with two stacked contact blocks (one NO for the K1 path, one NO for the K2 enable). The ELMARK EL2-BW07 accepts up to three stacked 1NO or 1NC contact blocks; use two 1NO blocks for the cleanest implementation.

If the panel has only one contact block, you can run both K1 and K2 from the same NO contact by adding a 100 Ω + 100 µF DC electrolytic + diode bridge to the K2 line to create a delayed pickup from a single PB event. The 100 µF cap charges to 80 % of 230 V peak (184 V) in t = R × C × ln(1/(1-0.8)) = 100 × 100e-6 × 1.6 = 16 ms. That is too fast — increase R to 2.2 kΩ for t = 350 ms. The capacitor must be 400 V DC-rated, and the diode bridge is 1N4007 (1 A) in a 600 V-rated package.

6.3 Schematic Overview

Operation:

• Tap (50-150 ms): K1 picks up and latches via K1 NO + K4 NC. K2 has not yet had time to pick up (RC = 150 ms). Lamp ON.
• Hold (700 ms+): K1 picks up and latches. K2 picks up at ~150 ms. K3 picks up at ~350 ms. K4 picks up at ~700 ms. K4 NC opens. K1's latch path is broken. When PB releases, K1 de-energizes (no path). Lamp OFF. K2, K3, K4 release sequentially over the next 1-2 seconds as their C's discharge.

6.4 Tuning the Cascade

The pickup delays above are nominal. Real G2R coils have ±10 % resistance tolerance, and X2 caps have ±5 %, so the cascade needs bench tuning. Procedure:

1. Power the K2 branch alone (with K1 contact replaced by a manual jumper). Adjust R2 until K2 picks up at exactly 150 ms after applying 230 VAC. Use an oscilloscope on K2's coil and a stopwatch on a digital timer triggered by the AC line zero-cross.
2. Repeat for K3 (target 350 ms) and K4 (target 700 ms).
3. Wire the cascade. Press and hold PB. Verify K4 picks up and K1 releases within 800 ms.
4. Tap PB (release in < 100 ms). Verify K1 latches and K2-K4 do not pick up.

7. Method 4 — Commercial Latching Relay Module

If the goal is simply to toggle a light with a single push button and you do not need to demonstrate the relay timing, the simplest engineering choice is a commercial latching relay module. One G2R is then used as the output stage.

7.1 Pre-built Pulse Latch Modules

Vendors such as Finder, ABB, and Schneider sell single-button latching modules in DIN-rail enclosures. The Finder 13.21 is a 12-24 VDC latching module with a single input pulse; the Finder 13.01 is the 230 VAC version. These accept one push button input and drive a relay output with toggle semantics. You then use one of your G2R-1-SN(S) as the actual load switch:

+-------+    +-------+    +--------+    +--------+
| 230V  |-->| F1 1A |-->| Finder |-->| G2R   |-->| LAMP  |
| L     |    |       |    | 13.21  |    | 1-SN  |    | 230V  |
+-------+    +-------+    | 12VDC  |    | (S)   |    +--------+
                          | latching    | 230V   |
   PB (NO) --------------->| module  |   | coil   |
                          +-------+    +--------+
                              |             |
                              +------+------+
                                     |
                            12 VDC SMPS 500 mA
                                     |
                                    230V N

Pros: 30 lines of wiring, no timing chain, no X2 caps, reliable across temperature and coil tolerance. Cons: 1 DIN rail module cost is ~3× the cost of one G2R.

7.2 Mechanical Latching Relay

Omron's MM2P and MM4P series are mechanical latching relays with two coils: a set coil and a reset coil. A single pulse on the set coil closes (or opens) the contact, and the contact stays in that state with no holding current. A subsequent pulse on the reset coil returns the contact to the original state. This is the true mechanical equivalent of a flip-flop. Two 24 VDC pulses, one push button, debounced by a 555 timer or by a 74HC123 monostable. The Omron MM2P-P-DC24V is rated 5 A at 250 VAC, 100,000 operations mechanical, 50,000 electrical. Datasheet: Omron MM2P/MM4P Datasheet (J23-E-02).

7.3 Push-On/Push-Off Push Button

The simplest answer to the original question is to replace the EL2-BW07 (momentary NO) with an EL2-BW07 + 1CO latching contact block, or buy an ELMARK EL2-BL07 maintained-action push button. These mechanically hold the actuator in the depressed position, so the first press closes the contact and the second press (with mechanical interlock release) opens it. Two wires run from the push button to the G2R coil, the G2R switches the load, no flip-flop required. This is the standard industrial solution for a one-button lamp toggle when you do not need a separate status output.

8. Method Comparison

9. Wiring Practices, Fusing, and Coil Suppression

All four methods share the same mains-side practices:

• Branch-circuit protection. 1 A fast-blow fuse (F1) on the switched L conductor to the relay load contact, sized for the bulb's inrush × 1.5. For a 100 W halogen, F1 = 1 A is sufficient. For a 500 W halogen, F1 = 5 A slow-blow (type T).
• Contactor separation. Mains wiring (the F1, K1 load contact, lamp, and 230 VAC relay coils) inside the enclosure must be physically separated from the low-voltage control board (CD4013, 2N2222, R-C timing). Maintain 50 mm creepage distance; use slotted wiring ducts; route mains in red/brown insulation, neutral in blue, ground in green/yellow.
• Coil suppression. The K1 and K2 AC coils produce 200-300 V inductive transients when interrupted. Across every 230 VAC coil, install a snubber: 100 Ω ½ W in series with 100 nF X2 (or use a commercial RC snubber such as the C252D by TE Connectivity). This extends the AC coil's release time slightly (helps the timing in Method 2/3) and reduces radiated EMI.
• Ground. The enclosure, the SMPS chassis (if metal), and the lamp fixture's protective earth must be bonded to the mains PE. The neutral is the return conductor for both the load and the relay coils — never use PE as a return.
• Surge protection. If the lamp is outdoors or in an industrial switchboard with inductive load sharing, add a metal-oxide varistor (MOV) across K1's load contact: e.g., Littelfuse V275LA40A (275 Vrms clamp, 6.5 kA surge). This protects K1's contact from indirect lightning surges on the supply.

10. Verification and Functional Test Procedure

Before connecting the lamp load, verify the control board on an isolated bench supply:

1. Power-on test. Connect 12 VDC to the CD4013 board. With PB not pressed, verify Q = 0 (K1 coil de-energized, lamp output OFF).
2. Single-press toggle. Press and release PB in < 200 ms. Verify Q = 1 (K1 energizes), and stays at 1 after release.
3. Second press toggle. Press and release PB again. Verify Q = 0 (K1 de-energizes).
4. Bounce test. Press PB 50 times in 5 seconds (mechanically bouncing contact). Verify Q toggles exactly 50 times (CD4013 with 100 nF debounce).
5. Brown-out test. Reduce 12 VDC supply to 9 V (75 % of nominal). Verify Q holds state (the G2R DC12 must-release is 10 % = 1.2 V; the CD4013 is rated down to 3 V; the 2N2222 saturates at Vce(sat) = 0.2 V at 50 mA). At 9 V the G2R coil sees 9 V, well above must-release.
6. Hot-load test. With the lamp connected, leave the lamp ON for 1 hour. Measure the G2R contact temperature with a thermocouple. For 100 W at 10 A rated contact, the temperature rise should be < 30 °C above ambient. If it is > 50 °C, derate to 80 % of rated load or use a contactor rated for switching duty (e.g., Omron G7L).
7. Endurance test. Cycle the load 1,000 times (1 Hz, 50 % duty). Inspect the relay contacts for pitting. For a 100 W incandescent load, expect < 0.1 mm of material transfer after 1,000 operations; the G2R is rated for 100,000 at this load.

11. Troubleshooting Matrix

12. Frequently Asked Questions