The robot wore a small solar panel on top of its fist-sized body, and sat in the middle of the room, like a dog basking in the sun.

"It'd be cool if Rover could store all that solar energy in a battery, then hide the battery in its cave for later.  Like a squirrel hiding nuts for winter."

My son had lots of good ideas.  "Yeah, that would be nice.  I wonder how we could do that?"
"There's an old battery charger in the cupboard.  Rover could use that to charge the batteries, then take them to his hideout."

I rubbed my chin.  "Yeah, I've got some cool new batteries.  He could certainly charge them up in the sun.  But purposeful movement, shifting items around, is much harder."

The clouds moved across the sky and we could see the motes in the sunbeams floating across the room. The robot inched after the moving light, the plastic paddles it used for feet stepping up and down.

"Hey, Dad.  If Rover could charge up his batteries in the moonlight, then he could run about all day long."

"You have great ideas, but when are you going to make them reality?"  I ruffled his hair.  He was a good kid, and tinkering with robotics might get his brain working and his grades up.

Jake's cell phone went off.  Ten years old with a phone.  I shook my head.

Rover was steadily moving across the wooden floor, following the sun.  Every now and then, the robot stopped, made a half turn, and checked that the darkest area in the room really was behind it.  "Great light-seeking behaviour," I said.

Then we watched as Rover walked into a table leg.  Rover immediately reversed its motor and withdrew six inches, paddling backwards across the floor.  Then he sat still, waiting, like an obedient dog.

"Now what," said Jake.  "Is he going to stall?"

"He's looking.  He's in dim light, he should be looking for somewhere brighter; he's a photovore."  I waited expectantly.  "Come on Rover, you can do it."

A shadow fell across the robot, and Rover twitched its feet and reacquired the sunbeams.  "Got it!" I was pleased with that response.  "That's great movement from one behaviour to another."

A door banged and a woman wearing a black leather skirt and a white fur coat walked in.  Her stiletto heels rang on the floor.  Rover forgot all about the sun and paddled across to the darkest corner of the room, turned around and waited.

"You spooked him," I told Melisa.

"I don't suppose you've fixed the Range Rover.  I'm going out to dinner."

"That beast of a vehicle needs an upgrade in one of its microprocessors.  Otherwise at some indeterminate point, the power steering will fail, and it will be considerably harder to steer, particularly around corners."

"I'll get a cab."  Melisa turned and flounced out of the room.  

Jake blinked his eyes, and waved his hand in front of his nose.  "Sheesh, what's she wearing as bait."

"It's a new fragrance called Gold Digger."

"Smells like wee."

"Probably is, but packaged and managed in the right way, rich women will buy anything."

"But you can't buy love, right?"  Jake walked over to Rover, who backed further into the corner.  He put out his hand to pick up the robot, but Rover turned one way and then another, evading the boy.  I had to come over and scoop up the robot using a grab arm I had designed just for the job.  "He's trying to avoid your shadow.  I really should have built in a stop signal; a couple of hand claps or something."

"No, Dad. Rover would be too easy to turn off.  I like him just the way he is."

I turned Rover over and checked the layers of circuit boards and LEDs and other sensors. 

"He has three senses: vision, sound and touch.  How can we add smell?"

"So he really would be like a dog?  Cool!"

I smiled.  "Easy to say, but aroma detection would be tough.  In animals, smell is all about chemicals binding to receptors on sensory neurones in the olfactory epithelium of your nose.  Then the neurones fire action potentials, which are a really quick flow of ions across the cell membrane, and the impulse propagates down the nerves into the brain, and then..."

"And then what, Dad?"

"And then the mystery of consciousness.  How does a bunch of electrical currents become the smell of perfume?"

"You know what would be really cool?"  Jake was thinking again, with a serious look on his face that I loved.

"I've no idea."

"If we could give Rover a tent, and then when he needed to hide, he could deploy the tent and hide in there."

"You are full of great ideas!  I love it.  We'll have the most amazing battery-charging, perfume-sniffing, tent-dwelling autonomous robot in the world."

I flicked the switch on Rover's battery compartment to off.  There was room on the chassis for one more circuit board.  I placed Rover on a stand on my desk, so his feet-like paddles were free and he couldn't wander off anywhere.

Jackie looked back at me in the photograph.  Jake's mother had decided that taste was the finest sense of all, and had devoted her life to the bottle.  It was in Melisa's favour that she didn't drink.

The garage door was rising up.  I heard the Range Rover start up and the enormous machine pushed out on to the drive. 

"I thought she was taking a cab?" said Jake.

"Maybe she really wants to test her upper body strength at high torque when the power steering on that monster gives out on a corner."

Melisa abandoned the Range Rover outside the front door.  A yellow cab pulled up at the end of the long drive.  She turned to where we watched from the workshop window and blew us a kiss.

"That leather skirt really is tight, Dad."

"Yeah, it really is."  I switched off the light.  "Come on, son.  Ready for your powering down routine."

***

The next day Melisa announced that we were having a party in the evening.  I protested, because of the short notice, and the fact I don't like parties much, but she insisted.  "Everyone's said yes."  She put her hand through mine.  "All my friends are dying to meet the famous inventor."

"And Jake too, of course?"

Melisa stopped short of rolling her eyes.  "Of course.  The darling boy can come down for a bit."

I disentangled my hand from hers and went back to my workshop.   Jake came in.  "We're having a party, Dad!"

"Yes, we are."

"You don't look happy. "

"I'll be happy if you're there."  I smiled at him.  "I'll make sure there's lots of ice-cream for us."

"Cool!" Jake left, bouncing his football down the hallway; that annoyed Melisa too.

I sat down at my desk with Rover on his stand.  I thought about taste and smell and the chemistry and physics of it.  Then I started rummaging around in the cupboards.  Any piece of broken or outdated electronic or motorised equipment got chucked in there.  I found an unopened breathalyser tube, the type you have to take on vacation in France and use to test yourself before braving the Gendarmerie.

The tube contained sulphuric acid to bring the alcohol vapour out of the breath into solution.  Then the alcohol turned the red-orange potassium dichromate into green chromium sulfate.  The colour change was detected by photocells, but user input was required to compare to a blank and get the reading above or below the legal limit. 

Still, the tube could be used in a simple stimulus-response circuit.  Everything about Rover was simple, analogue, reaction circuitry.  Detect this, do that; bump into something, go the other way; see something you like; go for it!  Soon the robot looked like it had a mind of its own, when in fact its circuitry was drawn on a single sheet of legal pad pinned on my workshop noticeboard.