Traps for young players

tommo_NZ

New Member
Hi Y'all, I have spent months writing code to run my irrigation system and was using Sertxd(..) to debug. When I programmed the chip it went all wrong. certain lines of a loop would not print and this pattern was repeated (same lines every time) identically every time I programmed it even with minor alterations to the code to try to isolate the problem. Then I swapped the 9v battery for a plug pack and voila, it was perfect. Flat battery, had me fooled because the problem replicated itself every time.
My question is, what other stupid things have trapped users in a similar fashion. What has had you chasing your tail only to wake up at 3:00 am and suddenly think "you dumb bugger, of course it ...." etc. etc. Maybe I will learn something.
 

manuka

Senior Member
Trust you went using the FULL 9V supply ?! PICAXE's supply limit is nearer 5V -several AA cells are the norm. Stan.
 

inglewoodpete

Senior Member
A 9v battery does not have much stuffing. When you connect it to a linear voltage regulator, that 4v drop wastes 44% of the available power. Plus the quiescent current required by the regulator sucks it dry pretty quickly.
 

dennis

Member
I am certainly excluded from the "young player" but have made many mistakes. The toughest was a simple breadboard error in offsetting a connect to the track and connecting to the parallel track next to it. There was enough capacitance between the two for the circuit to intermittently work and it was only when I moved all the components to another breadboard that I found this elementary error !
 

StefanST

New Member
A 9v battery does not have much stuffing. When you connect it to a linear voltage regulator, that 4v drop wastes 44% of the available power. Plus the quiescent current required by the regulator sucks it dry pretty quickly.
Use the MCP1702 regulator instead of 78L05. Quiescent current Iqo is 2 uA and under 20 uA at consumption of 20 mA. Drop-out is 650 mV at 250 mA (at 20 mA it will be under 50 mV).Or use MCP1802 with shutdown function and max. 0.1 uA.
 

lbenson

Senior Member
Use the MCP1702 regulator instead of 78L05. Quiescent current Iqo is 2 uA and under 20 uA at consumption of 20 mA. Drop-out is 650 mV at 250 mA (at 20 mA it will be under 50 mV).Or use MCP1802 with shutdown function and max. 0.1 uA.
Good advice not to use the 78L05, but none of that will fix the problem that "A 9v battery does not have much stuffing."
 

erco

Senior Member
Any 7805 linear regulator just burns off the extra power as heat, so you're contributing to global warming as well as wasting batteries. The regulator essentially functions like a big dumb series resistor. The power/heat which dissipated/burned/wasted is directly proportional to the current, so the more current drawn, the more power wasted. But they are cheap & plentiful, so for very low-current applications (~10-15 mA) there isn't much power wasted, and I still use 'em in a pinch. Of course you can buy a variety of more efficient step-up and step down regulator modules off ebay for a few pennies, so it makes sense to hoard a few of those. I've started using Lipos and power bank circuits, which provide USB charging plus 5V step-up circuitry. Ten for $1.45! https://www.ebay.com/itm/123896931491
 
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Lenp

New Member
Watch out for unused input pins.
I spent a long time head scratching about an 08 pulse circuit that worked great in simulation.
There were several 08's running the same code with different pulse sequences. One at a time worked great, but with two or more running, they all staggered like a drunk. You should always do something with those spare pins. Pull them up or down, not floating or they'll act like antenna's that get signals from the devil!
 

premelec

Senior Member
Signals from the devil are a good source of random non-repeating values - just don't let them kill the device function... ;-0
 
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