ruru67 wrote:lj wrote:
the teletype machine does NOT need lots of current to make it work, the receive circuit is NOT a solenoid. The input interface is a 20mA current loop and needs DC current up to 20mA. Current loops generally have a low current , usually 4mA for the "off" (= 0) condition, and 20mA for the "on"(=1) condition, the desired code being a binary sequence. The use of a non-zero "off" current allows for proof the connection is operational and not sending a long row of "0".
Oh, please. I restored the thing, I know how it works. The receive circuit is a solenoid; the main power, and all the timing comes from a constantly running shaft powered by an electric motor, while the solenoid initiates the receive cycle when a start bit is received and positions things according to the incoming data bits, so the print drum will be in the right place when the hammer whacks it into the ribbon and paper.
according to a document labelled 6354WD, (link
http://www.virhistory.com/navy/tty/tty-wd-list.htm ) the input circuit for a Type 33 Teletype comprises a load resistor for the current loop, which can either be 8mA=1 or 20mA=1, zero current being the 0 (unusual but never mind) feeding into a pair of transistors Q1 and Q2 switching a regulated 500mA supply to the solenoid.
I am very happy to discuss electronic/electrical matters. Was I rude ? perhaps ? but we see so many posts from people lacking in a clear understanding of what they are doing, and part of our job as Moderators or Members, is to point out risks. Unfortunately you have shown that you don't fully understand your restored Teletype, and perhaps that may carry over into other areas of your electrical expertise ?
As to the original subject, if you are willing to take risks with DIY electro-play, you need to do a number of things to improve safety.
Surface contact is generally high resistance, >1000R, often >50KR, TENS use conductive rubber pads, and the supply is itself high impedance, so you can't exceed a safe current.
Internal body contact (mouth, penis and anal) contacts are potentially very low resistance, well under 1000R, as are sub-epidermal contacts with needles or other puncture methods. It is essential that series resistors are used, calculated to limit the possible current to less than 20mA even if short-circuited.
Any contacts should not be placed such that the direct path between them crosses the heart (central and a lot higher up the chest than most people think) - that's where you apply defibrillator pads with the obvious reason - to disrupt the heart rhythm.
Any electrical shock may cause spasm, which could throw the victim into a dangerous situation.
There are various components (zener diodes, Transient Voltage Suppressors for example) which can be used to limit the maximum voltage that can be applied, caused typically by a random waveform such as audio through an inductive circuit. Coupled with a suitable series limiting resistor this would make the equipment relatively safe, but you would need an oscilloscope to determine the actual voltage swing across the likely load to get the values right.
It is generally accepted that any electrical equipment used in SB etc should be powered from an intrinsically safe supply - batteries rather than mains, isolation transformers, mains-failure to safe conditions, residual current breakers to prevent mains/earth faults.
But I repeat, don't mess with electricity unless you know what you are doing. Just the same as not messing with rope/chains/hoods/gags unless you are very careful. Life has risks, 100% sure to end in death, we just try to avoid it happening by ignorance, carelessness or unnecessary risk taking.