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By ROBERT SCOTT Cranial Electrical Stimulation Unit Commercial cranial electrical stimulation (CES) units cost hundreds of dollars but this one is cheap and easy to build. It is battery-powered, portable and has adjustable current delivery and repetition rate. N O, THIS IS NOT a do-it-yourself electroshock therapy project. The voltage and current used for Cranial Electrical Stimulation (also known as Transcranial Electrotherapy or Neuroelectric Therapy) is very low, ensuring that it is safe for the recipient. It does not cause a “shock” sensation or a lot of pain, although it can result in “pinpricks” at the higher settings. However, at the voltage and current levels involved with this project there is no risk of injury. We are not doctors so we can not say whether CES is beneficial. Some claim that it reduces anxiety, treats pain (especially headaches) and promotes alertness and relaxation. If you have investigated the potential benefits and would like to try CES, building this project is a cheap and easy way to do so. 26  Silicon Chip We can’t rule out the possibility that the benefits from CES are a placebo effect but if true, such benefits are still real. If so, it would be a case of “mind over matter!” What is CES? CES involves passing a small amount of current through the recipient’s head. A proportion of this is thought to pass through the brain and create chemical changes which may influence mood. Obviously we must be careful to limit the amount of power that can pass through a sensitive organ like the brain. In this case, the current is limited to a maximum of half a milliamp (0.5mA) and the voltage is limited to 15V. Since the unit is powered from a small battery (four AAAs) rather than mains, there is no possibility that a fault could result in a fried noggin! Commercial CES devices vary but generally deliver somewhere between 0.01mA to 1mA with a repetition rate between 0.5Hz and 100Hz. With this unit, both parameters can be adjusted, so you can find the combination that works best for you. The Transcutaneous Electrical Nerve Stimulation or TENS unit published in SILICON CHIP, January 2006 is similar in some respects. That unit also relied on electrical stimulation of the human body but at higher voltage and current levels. However, as stated in the TENS article, these levels are unsuitable for use on the head or neck, so this CES unit has been designed to deliver much less power in order to make it safe. Current is delivered to the patient via clip-on leads that attach to the siliconchip.com.au The Cranial Electro-Stimulator is built into a low-profile instrument case and is powered by four AAA 1.5V cells. ear lobes. While at first it may seem unlikely that just 15V can result in current conduction through the human body, the ear tingling and (at higher settings) pin-prick sensation demonstrates that a circuit is indeed made. Just how much current is flowing is indicated by the brightness of two LEDs on the front panel. For further evidence that a voltage this low can cause current to flow through the human body, set a DMM to Ohms mode and hold a probe in each hand. This will show your own body’s resistance, which varies depending on the amount of moisture on your hands. You should find that holding the probes behind your ears results in a similar reading. Generally you will find it is below 1MΩ. Circuit description Take a look now at Fig.1 for the circuit details. It’s based on four CMOS digital logic ICs and a handful of other parts. The ICs are readily available and since the circuit is based entirely on discrete logic, there is no need for a microcontroller. IC3 and IC4 form the on/off switch logic and session timer. They also flash the “RATE” LED at 1Hz to indicate that the unit is operating. IC3 is a 4011 quad 2-input NAND gate and IC4 is a 4040 siliconchip.com.au 12-stage binary counter. IC3a and IC3b together make an RS flip-flop. Pin 1 is its Reset input and pin 6 is its Set input. When pin 1 is pulled low (ie, button S1 is pressed), the output at pin 4 goes low and when pin 6 is pulled low (ie, button S2 is pressed) it goes high. When the ON button (S1) is pressed, the output of the flipflop goes low and this turns PNP transistor Q1 on. As long as Q1 remains on, power from the battery can flow to the rest of the circuit. Pressing S1 also resets IC4 (via IC3d), starting the session timer. The 10kΩ pull-up resistor and 100nF capacitor across S1 form a filter which debounces the button press and also ensures that the device is off initially when the batteries are installed. Note that IC3 is permanently connected to the battery but since it draws well under 1µA, its current draw is less than the cells’ self-discharge current. IC4’s clock input (pin 10) is driven Main Features • • Adjustable current (0.03-0.5mA) • • • • Battery powered Adjustable repetition rate (0.5    100Hz in four steps) Portable Flashing activity LED Automatic turn-off timer (25     minutes) which can be reset • LEDs indicate intensity of stimula   tion • Long battery life (up to 100 hours    continuous operation) at 2Hz (by pin 3 of IC1) so after 25 minutes of operation, outputs O10 and O11 (pins 15 & 1) of timer IC4 both go high. As a result, IC3c’s output goes low, pulling down pin 6 of IC3b which has the same effect as pressing Warning! (1) This unit (or any other similar device) must not be used on a person who has a Heart Pacemaker or other implanted electronic device. (2) Do not be tempted to run this unit from a mains adaptor, plugpack or power supply. This could be dangerous if a breakdown occurs in the isolating transformer. January 2011  27 28  Silicon Chip siliconchip.com.au 2011 1k 10 6 5 2 1 13 12 10k 7 IC 3c IC 3b IC 3a IC 3d 14 8 9 4 3 11 11 10 MR CP 100nF SESSION DURATION TIMING 6.8k B O4 O3 O2 O1 O0 2 3 5 6 7 9 8 Vss 13 15 14 O11 O10 O9 O8 O7 16 Vdd O4 O3 O2 O1 O0 K 10 7 4 2 3  LED1 A 1.5k 8 O5-9 12 O9 O8 O7 O6 11 9 6 5 IC 2 4017B O5 1 Vss C P1 MR C P0 1 15 14 12 13 IC 4 O5 4040B O6 4 16 Vdd CRANIAL ELECTRO-STIMULATION UNIT 100nF IC 3: 4011B 100nF C 220k 1k C E K  LED2 A 4.7k B A K 12 9 11 OSC o MR A K 13 15 1 2 3 15k A K B 8 Vss D1 E C 7 A 5 4 6 ZD1 D5 K 4.7k C Q3 BC 559 E B 10k 4.7nF A K A K K A LEDS K VR1 1M A K E D2 220 F 16V B C Q5 BC 547 B C E BC 639, BC 640 OUTPUT TO ELEC TRODES 100k E C 1 F C ON1 BC 547, BC 559 1M A K B +15V 10k LK4: 50Hz LK3: 100Hz LK2: 0.5Hz LK1: 1Hz OUTPUT INTENSITY 22k ZD1 15V D3 L1 (SEE TEXT) PULSE REPETITION RATE SELEC TION  LED3 A DC -DC C ONVERTER Q4 BC 639 O3 O4 O5 O6 POSITIVE & NEGATIVE PULSE FORMING & INDIC ATION 22k O9 O11 O12 O13 O8 IC 1 4060B O7 14 OSC i OSC o MAIN TIMING 12pF 10M 4.7nF D4 D1–D5: 1N4148 Q2 BC 559 100nF 33pF X1 32.768kHz 10 16 Vdd Fig.1: the circuit is based on four low-cost CMOS ICs. Quad NAND gate IC3 and 12-stage binary counter IC4 form the on/off switch and session timer, while 14-stage binary counter IC1 and decade counter IC2 set the pulse repetition rate. IC1 also forms a crystal oscillator (in conjunction with X1) and drives a boost converter based on Q4, inductor L1 and their associated diodes to produce a +15V rail. SC  OFF S2 ON S1 6V BATTERY (4 x AAA C ELLS) 1000 F E Q1 BC 640 Fig.2: the yellow trace shows the 32.768kHz waveform from the crystal oscillator at pin 10 of IC1. Below it, the green trace is the 512Hz signal at pin 4. The two lower traces show the alternating output pulse at pins 2 and 3 of IC2. As can be seen from the measurements, the output frequency is 102.5Hz (nominally 100Hz) and the duty cycle is 20%. the OFF button (S2). As a result, the RS flipflop is set and so Q1 turns off, powering down the circuit. Pulse timing Pin 9 of IC4 (O0) is the lowest timer output bit and this toggles at half the input clock rate, flashing high-brightness red LED1 at 1Hz while ever IC1 is powered. The 2Hz source clock is produced by IC1, a 4060 14-stage binary counter. Pins 10 and 11 of IC1 form a crystal oscillator circuit based on X1, a 32.768kHz watch crystal. Now 32,768 is 215, so a binary counter can derive exact 1Hz pulses from this frequency by dividing it in half 15 times. Since IC1 is a 14-stage ripple counter, it produces a 2Hz output at O13 as well as 4Hz at O12, 8Hz at O11 etc. Depending on which of LK1-4 is shorted, one of IC1’s clock outputs drives the base of Q5, an NPN transistor which acts as a level shifter. This allows IC1 – which runs from a 6V (nominal) battery – to interface with IC2 which runs off a higher voltage (15V). When Q5 is off, a 100kΩ resistor pulls pin 14 (CP0) of IC2 high to 15V. Conversely, when Q5 is on, that pin is pulled low to 0V. CP0 is the clock input of IC2, another counter IC. This one is configured to divide its input frequency by five, since its sixth output (O5) is connected to its reset pin (pin 15). Depending on which of LK1-4 is installed, IC2 is siliconchip.com.au Fig.3: these are the same signals as shown in Fig.2 but with a shorter timebase so that the 32.768kHz sinewavelike oscillation of the crystal is visible. As can be seen, when the first output pulse ceases the second immediately begins, causing a voltage differential across the electrodes. The output amplitude, as shown, is just below 15V driven at 4Hz, 2Hz, 512Hz and 256Hz respectively. After being divided by five the result is 0.8Hz, 0.4Hz, 102.4Hz and 51.2Hz. These are the four pulse repetition rate options available, which we round to 1Hz, 0.5Hz, 100Hz and 50Hz for convenience. and ensures a fast switch-off. The 1kΩ series resistor limits the base current. The advantage of using a boosted supply rather than just more battery cells is reduced size and weight as well as a consistent voltage for cranial stimulation, even as the battery discharges and its voltage drops. Voltage booster Electrode drive IC1 does double duty by also driving a boost converter based on transistor Q4. Its pin 9 output (which is an inverted version of the clock signal on pin 10) drives Q4’s base. This works with inductor L1, diodes D3-D5 and zener diode ZD1 to generate a nominal 15V rail which powers IC2 and ultimately provides the cranial stimulation. In operation, the 32.768kHz square wave from pin 9 of IC1 is AC-coupled to the base of Q4, an NPN transistor with a 1A rating. When the output from pin 9 is high, Q4’s base-emitter junction is forward biased and so it “sinks” current from the battery through L1, a high-value inductor. This charges its magnetic field. When the output from pin 9 subsequently goes low and Q4 switches off, the collapsing magnetic field causes a voltage spike. This in turn forward biases D3 and charges the 220µF capacitor at its output. The voltage across this capacitor is limited to 15V by ZD1. D4 protects Q4’s base-emitter junction from being reverse biased, while the 15kΩ resistor provides DC bias As mentioned, IC2 divides its input clock by five. This means each of its O0-O4 output pins is high for 20% of the time and low the remaining 80% of the time. Two of these outputs (O0 and O1) drive the cranial electrodes while the other three are not connected. As a result, the electrodes are driven alternately, followed by a pause. Current for the electrodes flows from O0, through the recipient’s head and back to O1, or it flows the other way around. When one of these outputs is sourcing current, it passes through a 22kΩ resistor which provides current limiting. Alternatively when sinking current, most of the current flows through either diode D1 or D2. High-brightness LEDs Transistors Q2 & Q3 drive highbrightness blue and green LEDs to indicate which output is sourcing current and how much is flowing. The more current that passes through one of the 22kΩ resistors, the higher the base-emitter voltage of the associated transistor. January 2011  29 100nF 10k + 1000 F 1k 100nF S2 IC3 4011B S1 Q1 BC640 6.8k IC4 4040B – + L1 4.7mH 15k BC639 4148 A 100nF Q5 D3 (L1) LED3 K IC1 4060B 10k 100k VR1 1M 4148 A 1k D5 4148 10M X1 LK1-4 LED2 K 220k 32.768kHz 50Hz 100Hz 0.5Hz 1Hz LED1 K A 12pF 1 F D4 1.5k 33pF 4 x AAA CELL HOLDER Q4 BC547 IC2 4017B 4.7k 220 F D1 10k D2 CON1 Q3 22k 4148 BC559 4.7nF 4.7k Q2 22K 4148 15V 4.7nF ZD1 + 100nF BC559 LINK FROM TAB TO BOARD 1M Fig.4: follow this layout diagram to assemble the PC board. Make sure that all polarised parts are correctly orientated and be careful also not the get the ICs mixed up. The photo below shows the completed prototype. 30  Silicon Chip These transistors drive high-brightness LEDs. Higher base-emitter voltages result in more current flow to these LEDs and thus they glow brighter. A 4.7nF capacitor across each base-emitter junction prevents AC signals coupled via stray capacitance (primarily within Q2 and Q3) from turning on the LEDs when there is no electrode current. Note that there is additional resistance between output O1 and the electrodes, as compared to the path from O0. This consists of a series 10kΩ resistor and 1MΩ potentiometer (VR1), with a 1MΩ fixed resistor in parallel with the latter. The 10kΩ resistor provides additional current limiting while VR1 allows the stimulation current to be adjusted from approximately 0.03mA to 0.5mA. Inductor selection The inductor (L1) used in the prototype was obtained from a nonfunctioning compact fluorescent lamp (CFL). If you have a faulty 15-20W CFL, you can open it up by clamping the base in a vice and then cutting through the groove in the plastic base using a hacksaw. Chances are it will contain a suitable choke. Be careful not to break the glass tube(s) during this operation. siliconchip.com.au If you do not have an unserviceable CFL to dismantle, a 4.7mH (or thereabouts) inductor with a current capability of at least 100mA can be substituted. These are available from Altronics (Cat. L7054). Alternatively, if you have an inductance meter, you can wind your own inductor on a ferrite or powdered-iron core – just add turns until the measured inductance is in the appropriate range. The salvaged inductor in the prototype measured 7mH. The lower the inductance value used, the higher the battery drain when the unit is operating, as the peak current through L1 is higher. A 4.7mH inductor increases the battery current by around 2mA compared to using a 7mH inductor. For this reason, we do not recommend going much lower than 4.7mH. Another view inside the prototype. Note that, for safety reasons, this unit must be powered by four AAA 1.5V cells. Do NOT use a plugpack. Construction All the parts are mounted on a single-sided PC board coded 99101111 and measuring 118 x 102mm. Fig.4 shows the assembly details. Begin by checking the board for any defects, then fit the resistors. Use a digital multimeter (DMM) to check the value of each resistor before installing it. Once they are in, follow with the diodes (D1-D5) and zener diode (ZD1). Ensure that the striped end of each diode is orientated as shown on Fig.4. Follow with the ICs, taking care to ensure that each is correctly orientated and that it is installed in the correct location. Alternatively, if you are using sockets (optional) then install them instead. In either case, the notch or dot that indicates pin 1 goes towards the back edge of the board. Check also that each device is sitting flat on the PC board before soldering its pins. Do not get the ICs mixed up, as they are all different types. Crystal X1 is next on the list. It doesn’t matter which way around it goes. Lay its body flat against the PC board using a small piece of doublesided tape to hold it in place, to avoid stress on the leads. Next mount the five transistors (Q1-Q5). There are four different types so check the marking on each before installing it, to ensure it goes in the right place. Use small pliers to bend the legs outwards at 45° and then back down parallel again so that they fit in the holes on the board. Be sure to orientate each one as shown on the overlay. Now solder the MKT and ceramic capacitors in place, followed by the pin header strip and the two electrolytic capacitors. The electrolytics must be correctly orientated, so be sure to match their positive (longer) leads with the “+” signs on the overlay. Follow with the two tactile switches, which must be pushed flat against the PC board before being soldered. The 3.5mm jack socket is not a PCmount component so this must be modified before it is installed. First, use pliers to pinch the eyelet holes shut, except for the longer one projecting from the rear of the connector. That done, bend the shorter lead at the rear down at right angles (see photo). Table 2: Capacitor Codes Value 1µF 100nF 4.7nF 33pF 12pF µF Value IEC Code EIA Code 1µF 1u0 105 0.1µF 100n 104 .0047µF 4n7 472 NA 33p    33 NA 12p    12 Table 1: Resistor Colour Codes o o o o o o o o o o o o siliconchip.com.au No.   1   1   1   1   2   1   3   1   2   1   2 Value 10MΩ 1MΩ 220kΩ 100kΩ 22kΩ 15kΩ 10kΩ 6.8kΩ 4.7kΩ 1.5kΩ 1kΩ 4-Band Code (1%) brown black blue brown brown black green brown red red yellow brown brown black yellow brown red red orange brown brown green orange brown brown black orange brown blue grey red brown yellow violet red brown brown green red brown brown black red brown 5-Band Code (1%) brown black black green brown brown black black yellow brown red red black orange brown brown black black orange brown red red black red brown brown green black red brown brown black black red brown blue grey black brown brown yellow violet black brown brown brown green black brown brown brown black black brown brown January 2011  31 Parts List For Cranial Electro-Stimulator 1 PC board, code 99101111, 118 x 102mm 1 ABS instrument case, 140 x 110 x 35mm (Jaycar HB-5970) 1 PC-mount 4 x AAA battery holder (Jaycar PH-9270) 2 right-angle tactile switches (Jaycar SP-0607) 1 3.5mm mono phono jack socket (Jaycar PS-0122) 1 3.5mm mono phono jack plug (Jaycar PS-0114) 1 knob to suit VR1 1 4700µH inductor (Altronics L7054) or higher value choke salvaged from a CFL (L1) 1 32.768kHz watch crystal (X1) 1 2 x 4-pin header, 2.54mm pitch 3 16-pin DIL sockets (optional) 1 14-pin DIL socket (optional) 1 jumper link for pin header 1 pair 65mm alligator clips 3 right-angle LED mounting blocks (Jaycar HP-1114, packet of 20) 4 No.4 x 6mm self-tapping screws double-sided tape 100 x 12 x 0.127mm (0.005inch) brass sheet 1 2m-length twin core cable 25mm 0.71mm diameter tinned copper wire 25mm heatshrink tubing, 5mm diameter 1 front panel label 1 1MΩ 16mm linear potentiometer (VR1) 2 M2 x 5mm machine screws & nuts Next, solder a piece of tinned copper wire to the remaining eyelet, making sure it is long enough to go through the PC board. That done, push the two leads through the board and solder the connector in place. The LEDs go in next. Their leads must be bent down at right-angles 5mm from the lens but first check the orientation. In each case, the longer The ear electrodes are made up by soldering U-shaped brass pieces to alligator clips (after the jaws have been filed off). mounting thread). File off any burrs before mounting it on the PC board. Finally, attach the battery holder to the board using M2 machine screws and nuts. Alternatively, if these are not available, it can be held down using double-sided tape. Once it is firmly attached, solder its pins. Resistors (0.25W 1%) 1 10MΩ 3 10kΩ 1 1MΩ 1 6.8kΩ 1 220kΩ 2 4.7kΩ 1 100kΩ 1 1.5kΩ 2 22kΩ 2 1kΩ 1 15kΩ Making the electrodes lead goes through the hole marked “A” (anode) on the overlay. Once the leads have been bent, insert each through a plastic mounting block and attach this to the PC board using double-sided tape. Once they are in place, solder and trim the leads. Inductor L1 can go in next, then using a hacksaw, trim VR1’s shaft to 9mm (as measured from the end of its FLOW INDICATORS HI LO 32  Silicon Chip Capacitors 1 1000µF 10V electrolytic 1 220µF 16V low-ESR electrolytic 1 1µF monolithic ceramic 4 100nF MKT 2 4.7nF MKT 1 33pF ceramic 1 12pF ceramic The electrodes are made from a 100 x 12mm brass sheet and some alligator clips. First, cut the brass sheet into two 50 x 12mm strips, then bend each strip into a “U” shape using a thin piece of scrap wood fixed in a vice. That done, file the teeth off the alligator clip jaws and burnish the inner faces and edges with emery cloth. The U-shaped brass pieces can then be inserted into the jaws of the alligator clips and soldered in place (see photo). Next, trim and file away any excess at the edges, then use the emery cloth CRANIAL ELECTRO STIMULATOR SILICON CHIP OUTPUT Semiconductors 1 CD4060/HEF4060 14-stage ripple counter (IC1) 1 CD4017/HEF4017 decade counter/divider (IC2) 1 CD4011/HEF4011 quad 2-input NAND gate (IC3) 1 CD4040/HEF4040 12-stage ripple counter (IC4) 1 BC640 PNP transistor (Q1) 2 BC559 PNP transistors (Q2, Q3) 1 BC639 NPN transistor (Q4) 1 BC547 NPN transistors (Q5) 5 1N4148 signal diodes (D1-D5) 1 15V Zener diode (ZD1) 1 5mm high-brightness red LED (LED1, Jaycar ZD-0283) 1 5mm high-brightness green LED (LED2, Jaycar ZD-0176) 1 5mm high-brightness blue LED (LED3, Jaycar ZD-0281) LEVEL NEG POS RATE ON OFF Fig.5: this full-size artwork can be copied and used as a drilling template for the front panel. It can also be downloaded in PDF format from the SILICON CHIP website. siliconchip.com.au The electrodes plug into the output socket on the front panel. Also on the front panel are the on-off buttons, the current-flow indicator LEDs and the level control. to remove any sharp jags. Make sure the clips have no sharp protrusions then test them on your earlobes. If they are too tight, the tension can be adjusted by bending the spring. Once the clips are ready, solder them to one end of a 2m-long figure-8 cable, spreading it into a “Y” shape about 30cm from the end. That done, slide heatshrink tubing over the split and shrink it down, to prevent the cable from pulling apart further. Solder the wires at the other end of the cable to the two tabs of a 3.5mm mono phono jack plug. Alternatively, rather than making your own electrodes, you may be able to make use of ECG or TENS electrodes which can be bought from some pharmacies. Testing the board If you have a bench supply, set it to 6V with a current limit of approximately 20mA. Otherwise, use the four cells to power it for testing. If possible, it is a good idea to insert a DMM in series with the supply to check the current flow. Initially, leave the ICs out of their sockets (assuming they are not soldered to the board). Also check that the board is resting on a non-conductive surface. When the supply is connected, the current should be practically zero. If so, switch off and insert the ICs, then switch it back on. With the ICs in place, the current drain should be around 0.03µA. However, this is below the measurement range of most DMMs so they will read zero. If the current is significantly above the expected level, disconnect the supply and check for assembly errors. Now press the “ON” button and siliconchip.com.au watch the current reading. It should increase to around 8-10mA and the RATE LED should flash. When the RATE LED is on, the current reading will be slightly higher. Use a voltmeter to check the voltage between pins 16 & 8 of IC2 – it should be around 15V. If that checks out, turn VR1 fully anti-clockwise, plug in the electrodes and install the shorting block on LK1. Now temporarily connect the electrodes together (ie, create a short circuit) and slowly turn VR1 clockwise. LED2 and LED3 should now begin to flash alternately at 1Hz, getting brighter as VR1 is turned up. Finishing up Assuming it all works correctly, the board can now be installed in the case. First, use Fig.5 as a drilling template for the front panel. Start each hole using a pilot drill, then enlarge it to the correct size using larger drill bits or a tapered reamer, to ensure they stay round. Once the holes are made, check that they line up properly with the PC board. The front-panel label can now be prepared. You can either copy Fig.5 or download a front panel label in PDF format from the SILICON CHIP website. Once it is printed, laminate it and cut out the necessary holes, then attach it to the front panel using a thin smear of silicone sealant or spray adhesive. Leave the sealant to cure overnight before attaching the PC board assembly. It’s just a matter of feeding the board components through their corresponding front panel holes, then securing the panel by fitting the nuts to the output socket and potentiometer. The knob can then be fitted to the pot shaft. The U-shaped brass pieces ensure operator comfort when the electrodes are attached to the ear lobes Before the board can be lowered into the case, two plastic standoffs at the front of the case (towards the centre) must be removed. These can be filed away or cut off with large side-cutters. The board assembly can then be lowered into the case and secured in place using four self-tapping screws. Finally, install the jumper link on LK1-4, depending upon the repetition rate you want to use, and attach the lid. If you are not sure, start with 0.5Hz; you can always remove the lid later to try the other settings. Using it Before using it, turn VR1 fully anticlockwise. Attach the electrodes to the recipient (or yourself) and press the ON button. The RATE LED will flash at 1Hz to confirm that the device is operating. Now slowly turn up VR1. When the green and blue LEDs barely light, this indicates that around 25µA is flowing through the electrodes (and thus the recipient). At full power, around 500µA can flow and the LEDs will light brightly. As previously stated, the two LEDs indicate the current flow in each direction. We recommend the use of alkaline cells for this project as they last well in devices which draw a small amount of current over a long period and also have a good shelf life. That’s it. We hope that you find this project sufficiently stimulating SC (groan!). January 2011  33