Winch controller for boaties & 4WDers

Australia has a high percentage of domestic boat ownership, with over 600,000 registered owners in 2000. Winches are a necessary part of the gear and are typically used with boat trailers and on slipways. They’re also very popular on 4WD vehicles for use in the bush. Here is a companion winch controller that (with its remote control) will make your boat or 4WD ownership even more enjoyable.

Fig.1: the block diagram for the system. It controls the winch motor using two power relays.

At the heart of the design is a PICAXE micro, which receives "rope in", "rope out" and "all stop" commands via pushbutton switches or wireless remote control. In response, it controls the winch motor using two power relays (see Fig.1).

The complete circuit diagram for the winch controller appears in Fig.2. Looking first at the microcontroller inputs (P1, P3 & P4), these all originate from the pushbutton switches (S1-S3) and RF decoder (IC1) outputs, as well as the two limit switches (S4 & S5).

All inputs are "deglitched" with the aid of identical monostable circuits, comprised of one inverter gate and two NAND gates plus a few resistors and capacitors. The monostable circuits provide a clean, 100ms positive pulse to the associated PICAXE input when their inputs transition from high to low, ignoring subsequent switch contact bounce or spurious noise from the RF receiver outputs.

Two port pins of the PICAXE (P0 & P2) are configured as outputs to drive transistors Q1 & Q2, which in turn control two high-power relays. In the relaxed (normally-closed) state, the relay contacts short the motor terminals together; this is the "all stop" position.

When the "rope in" switch is pressed, the program sets output0 (P0) high and relay RLY1 is energised, connecting power to one side of the motor to retract the winch cable. Alternatively, when the "rope out" switch is pressed, output2 (P2) goes high and RLY2 is energised, reversing the direction of the motor and therefore releasing the winch cable.

Fig.2: the winch controller circuit receives and decodes the commands from the transmitter. These commands are then processed by microcontroller IC4 (PICAXE-08M) which in turn controls the motor relays.

Limit switches are used in this application to (indirectly) switch off the motor when the cable is fully retracted or deployed, to prevent excessive strain being placed on the winching system.

Limit switches should be used if the winch design supports them. To illustrate the need for these switches, imagine that the fishing is finished for the day and the boat has been winched into the shed. During winching, the "in" limit switch has opened, removing power to the motor. This switch now forms a kind of "memory", so that days later, when the winch is switched on again, it cannot be accidentally operated in the wrong direction.

Consider the "in" limit switch action, for example. Initially, with RLY1 energised, the winch will be running. When the cable fully retracts, the "in" limit switch (S4) is physically contacted, changing its pole to the alternate position and removing drive current to the base of Q1. This immediately de-energises the relay and switches off the motor.

Now in the alternate position, the switch contacts connect output0 of the PICAXE (P0) to diode D11 and the input of a monostable circuit. The result is a clean, positive-going pulse at input3 (P3) of the micro. On detecting the pulse, the BASIC program responds by taking output0 low and then waiting for the next command.

The signal path from output0 to transistor Q1 and the relay are now open circuit, preventing the "rope in" command from having any further effect until the "rope out" command is used to play out some slack. This safeguards against overrunning the limit switch. The "out" limit switch functions in the same manner.

If limit switches aren’t needed in your application, then all of the associated support circuitry can be omitted. This includes D11, D12, D8, IC3c, IC3d, IC5d, etc. The cathodes of diodes D9 & D10 are then connected directly to Q1 & Q2’s 1.5kW base resistors, respectively.

Fig.3: the transmitter is based on a pre-built RF module and is simple enough to build into a hand-held instrument case.

Fig.3 shows a 3-channel transmitter suitable for use with the winch controller. Low-cost Laipac (or sim-ilar) 433MHz RF transmitter and receiver modules are used for the remote control section. Button presses are encoded at the transmitter end using a SM5162 trinary encoder IC and decoded at the receiver end using the complementary SM5172 decoder.

The address pins on the encoder and decoder IC (not shown) can be connected to +V, 0V, or left open-circuit to create a trinary-based security code. Both the transmitter and receiver address pins must be wired exactly the same way.

However, you should leave all of the address pins open-circuit until you get the transmitter and receiver working properly. At the receiver end, a DVM can be connected between pin 17 of IC1 and ground for faultfinding purposes. On reception of a valid transmission (a button press on the remote), this pin should swing to a logic high (about +4.7V).

Once the units have been tested, the address pins should be coded to minimise the possibility of interference with other systems. Note that this remote control scheme operates identically to a number of garage door openers and the like that have been published in SILICON CHIP in recent years – eg, the 4-Channel UHF Remote Control described in the June 2003 issue.

Datasheets for the Laipac TLP-434 transmitter and RLP-434 receiv-er modules are available from www.laipac.com. Compatible 433MHz modules are available from all major kit suppliers. Oatley Electronics sells the encoder and decoder ICs (stock codes SM5162RF & SM5172RF). Check ’em out at www.oatleye.com, with datasheets available from www.samhop.com.tw.

For operation at 433.92MHz, a quarter-wavelength antenna needs to be 172mm long. If you are using a plastic case for the transmitter, then a 172mm length of wire may be wound into an oblong and glued inside the case. Alternatively, an extendable rod antenna could be used.

The receiver requires only a wire
cut to 172mm, although it too could use a rod antenna. With a little fine-tuning, a range of approximately 50-60 metres is easily obtainable.

Although greater range is possible by using more elaborate antennae, safety is an overriding factor. You should always be in visual contact with the winch and the load that is being winched, to guard against injury to others.

The PICAXE program for this application is self-explanatory. Of note is the use of the ’08M’s interrupt feature to detect positive transitions on input3, which can originate from the "all stop" switch or the limit switches.

Once up and running, check that the winch comes to a complete stop before reversing direction when the "rope out" and "rope in" buttons are pressed in quick succession. The length of the pause command in the Init: section of the program can be trimmed to ensure that this occurs.

Finally, the author recommends the use of high-quality pushbutton switches to ensure reliable, long-term operation. While the monostable circuits will remove switch contact bounce, they cannot compensate for faulty switch contacts!

;****************************************** 
;* 
;* Marine Winch Motor Control   V1.7 
;* 
;******************************************* 
; 
; NOTE: pin0 - pin4 are all active high 
; 
; Initialisation 
; 
setint %00001000, %00001000 		;interrupt when IN3 goes high 
b5 = 0					;interrupt Flag 
;
; Main program start 
; 
Init: 
low output0				;turn off IN relay 
low output2				;turn off OUT relay 
pause 1000				;motor pause - set to suit motor, 
;					;must allow motor to stop 
b5 = 0					;zero the interrupt flag 
; 
Exec:					;primary input
if b5 = 1 then Init			;has interrupted so init 
pause 10 
if Pin4 = 1 then WinchIn 
pause 10 
if Pin1 = 1 then WinchOut 
goto Exec 
; 
NextSwitch:				;secondary switch point 
if b5 = 1 then Init			;has interrupted so init 
pause 10 
if pin4 = 1 then Init 
pause 10 
if pin1 = 1 then Init 
pause 10 
goto NextSwitch
;
WinchIn:					;rope in 
if b5 = 1 then Init			;has interrupted so init 
high output0				;pull the rope in 
pause 300				         ;settle time 
goto NextSwitch 
; 
WinchOut:				         ;rope out 
if b5 = 1 then Init			;has interrupted so init 
high output2				;let the rope out 
pause 300				         ;settle time 
goto NextSwitch 

end					;should not get here! 
; 
Interrupt: 
low output0				;switch off IN relay 
low output2				;switch off OUT relay 
input3 = 0				;reset pin3 for next interrupt 
b5 = 1					;set the interrupt flag 
setint %00001000, %00001000 		;restore interrupt 
return

Pushbutton relay selector

This circuit was designed for use in a hifi showroom, where a choice of speakers could be connected to a stereo amplifier for comparative purposes. It could be used for other similar applications where just one of an array of devices needs to be selected at any one time.

A bank of mechanically interlocked DPDT pushbutton switches is the simplest way to perform this kind of selection but these switches aren’t readily available nowadays and are quite expensive.

This simple circuit performs exactly the same job. It can be configured with any number of outputs between two and nine, simply by adding pushbutton switches and relay driver circuits to the currently unused outputs of IC2 (O5-O9).

Gate IC1a is connected as a relax-ation oscillator which runs at about 20kHz. Pulses from the oscillator are fed to IC1b, where they are gated with a control signal from IC1c. The result is inverted by IC1d and fed into the clock input (CP0) of IC2.

Initially, we assume that the reset switch (S1) has been pressed, which forces a logic high at the O0 output (pin 3) of IC2 and logic lows at all other outputs (O1-O9). As the relay driver transistors (Q1-Q4) are switched by these outputs, none of the relays will be energised after a reset and none of the load devices (speakers, etc) will be selected.

Now consider what happens if you press one of the selector switches (S2-S5, etc). For example, pressing S5 connects the O4 output (pin 10) of IC2 to the input (pin 9) of IC1c, pulling it low. This causes the output (pin 10) to go high, which in turn pulls the input of IC1b (pin 5) high and allows clock pulses to pass through to decade counter IC2.

The 4017B counts up until a high level appears at its O4 output. This high signal is fed via S5 to pin 9 of NAND gate IC1c, which causes its output (pin 10) to go low. This low signal also appears on pin 5 of IC1b, which is then inhibited from passing further clock pulses on its other input (pin 6) through to its output (pin 4), thus halting the counter.

So, the counter runs just long enough to make the output connected to the switch that is pressed go high. This sequence repeats regardless of which selector switch you press, so the circuit functions as an electronic interlock system.

Each relay driver circuit is a 2N7000 FET switch with its gate driven from one output of IC2 via a 100W resistor. The relay coil is connected from the drain to the +12V supply rail, with a reverse diode spike suppressor across each coil.

If you want visual indication of the selected output, an optional indicator LED and series resistor can be connected across each relay coil, as shown. For selecting pairs of stereo speakers, we’d suggest the use of relays like the Jaycar SY-4052. These operate from 12V and have DPDT contacts rated for 5A.

Note that although four selector switches are shown in the circuit, only two relay drivers are shown because of limited space. For a 4-way selector, identical relay drivers would be driven from the O2 and O3 outputs of IC2.

SILICON CHIP.

Dual input-combining stereo line amplifier This circuit takes two separate line-level stereo (L & R) signals and combines them into one stereo (L & R) output, thus avoiding the need to switch between two pairs of input signals. In the author’s application, it is used to feed the stereo audio from a TV receiver and a DVD player into an external amplifier. The need for the circuit arose because of a design peculiarity in the TV receiver. The TV has four A/V inputs and one A/V output. AV1-AV3 accept composite or S-video plus stereo audio inputs and these feed into the TV’s A/V output. AV4 accepts Component video (Y/Pb/Pr) plus stereo audio but unlike AV1-AV3, its audio (and video) signals are not fed to the TV A/V output. The Y/Pb/Pr input was chosen for use with the DVD player because of its superior video quality, while the audio was to be fed to an external amplifier for improved reproduction. However, manual switching was inconvenient, hence the genesis of this design. In use, the DVD player audio is fed in parallel to TV AV4 and to one input pair of the combining amplifier, while the TV audio output feeds the other input pair. The amplifier output goes to the external audio amplifier. There is no conflict between the two audio inputs because when AV4 (DVD player) is selected, there is no TV audio output. In all other modes, the DVD player is off. As shown, the circuit has a voltage gain of 1.5 times (3.5dB) but this can be altered as required by changing the two 15kW resistors. Input impedance is 10kW and the outputs are isolated from cable and amplifier input capacitance with 47W series resistors. The circuit can be powered from a regulated 12V DC plugpack. Garth Jenkinson, Emerald, Vic. ($40)

Battery desulphation progress monitor

A number of readers have asked how to tell when the Lead-Acid Battery Zapper (SILICON CHIP, July 2005) has done its job and battery desulphation is complete.

In the author’s experience, batteries that are going to respond to this treatment will generally show quite a high peak voltage across the terminals at the beginning of the treatment. If this steadily decreases and practically disappears, then the treatment is near to complete. This may take anything from a week to many months, depending on the size and condition of the battery.

In the absence of an oscilloscope to monitor the voltage peaks, a simple peak detector can be constructed from a fast diode and 100nF capacitor. Any high-impedance multimeter (eg, most digital types) can then be used to measure the average DC voltage across the capacitor.

Nicad charger uses voltage cut-out

This circuit charges two NiCad cells with a constant current and features dual charging rates, voltage cutoff and an audible alarm.

The circuit is powered by a 12VAC centre-tapped mains transformer, together with two rectifier diodes (D1 & D2) and a 1000mF filter capacitor. A 7806 3-terminal regulator is used to generate a 6V rail for the remainder of the circuit.

Transistor Q1 and LED1 constitute a basic constant-current source. The forward voltage of the red LED (about 1.5V) minus Q1’s base-emitter voltage (about 0.6V) appears across the 6.8W or 15W emitter resistors, depending on the position of S1. With a 15W resistance in the emitter circuit, the charging current is about 60mA, whereas with 6.8W it is about 130mA. This is sufficient to charge 600mAH "AA" cells in 14 hours and five hours, respectively.

An LM393 voltage comparator (IC1) is used for the voltage cutoff function. Its inverting input is set to 2.9V (nominal) via trimpot VR1, while the non-inverting input senses battery voltage. This means that while the cells are being charged, the output transistor (in the LM393) is switched on, also switching on Q1 and enabling the current source.

Once the cells are charged to approximately 80% or more of capacity, their terminal voltages will exceed 1.45V, so the voltage at the non-inverting input (pin 3) of IC1 will exceed the reference voltage on the inverting input (pin 2). This causes IC1’s output to switch off, in turn switching Q1 off and disabling the current source.

To prevent rapid switching action around the voltage cutoff point, a 100nF capacitor provides feedback between the output and inverting input of the comparator.

Four NAND gates are used to build two simple oscillators of different frequencies. When cascaded together, the result is a pulsed tone from the piezo transducer to indicate charge completion.

Editors note: absolute terminal voltage is not always a reliable indicator of Nicad battery charge state. Importantly, batteries should never be charged for longer than the manufacturer’s specified period.